Systems and methods for the identification of compounds using admittance spectroscopy

ABSTRACT

Described herein are systems and methods for determining the location, composition and concentration of a hydrocarbon containing plume in environmental seawater. These systems and methods disclosed use multiple complex admittance measurements from seawater in order to identify the contents, concentration, and location of the hydrocarbon containing plume. In preferred variations system includes a sensor array that substantially simultaneously records plume location, depth, and composition.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims priority to U.S. Provisional PatentApplication Ser. No. 61/185,148 (titled “IV SENSING ITEMS FORPROVISIONAL PATENT APPLICATION”) filed on Jun. 8, 2009; U.S. ProvisionalPatent Application Ser. No. 61/230,057 (titled “MEASUREMENT ANDIDENTIFICATION OF IV FLUIDS”), filed on Jul. 30, 2009; U.S. provisionalPatent Application Ser. No. 61/240,835 (titled “APPLICATION OF MULTIPLESENSORS TO MEASUREMENT AND IDENTIFICATION OF DRUGS”) filed on Sep. 9,2009; U.S. Provisional Patent Application Ser. No. 61/262,155 (titled,“SYSTEMS AND METHODS FOR THE IDENTIFICATION OF COMPONENTS IN MEDICALFLUIDS THROUGH THE APPLICATION OF MULTIPLE ELECTRODE ADMITTANCESPECTROSCOPY”) filed Nov. 18, 2009; and U.S. Provisional PatentApplication Ser. No. 61/302,174 (titled “SYSTEMS AND METHODS FORMEASUREMENT AND IDENTIFICATION OF DRUG SOLUTIONS”) filed Feb. 8, 2010.

This application may also be related to PCT application serial No.PCT/US2009/001494 (titled “INTRAVENOUS FLUID MONITORING”) and filed onMar. 9, 2009.

All of these patent applications are herein incorporated by reference intheir entirety.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference in their entirety to the sameextent as if each individual publication or patent application wasspecifically and individually indicated to be incorporated by reference.

FIELD OF THE INVENTION

The devices, systems and methods described may be used to determine theidentity, concentration, and location of one or more components in anaqueous solution. In particular, described herein, are devices, systemsand methods for determining the identity and concentration hydrocarbonsor other contaminants in seawater.

BACKGROUND OF THE INVENTION

Oil and oil containing compounds occur naturally in the environment.Ground oil seepage exists in many parts of the world including the Gulfof Mexico and off the California coast. Additionally, to the extent thatoil is transported in seagoing vessels or removed from the earth usingoffshore oil rigs, oil will periodically spill into the environment,specifically the seas and oceans. Oil does dissipate with time, andwhile the exact mechanism is not a number of factors are believed tocontribute to the oil's apparent disappearance/environmentalassimilation. As stated, the full mechanism or mechanisms by which oilis dissipated is an open question. A better understanding of how oilbehaves in the sea may allow scientists to deal with the catastrophiceffects of accidental or deliberate man made oil spills.

Oil in the environment can form micro-bubbles with relatively largesurface to volume ratios, this may be especially so when surfactants aremixed the oil. These micro-bubbles form an emulsion in the seawater andcan create significant underwater oil plumes. Some oil, by virtue ofother mechanisms, composition and other factors form other sub-surfaceoil formations, both in the emulsion class and in other classes. Theseplumes can cover significant areas and can have serious consequences foranimal and plant life which come in contact the plume.

Certain biological species are voracious consumers of the oilmicro-bubbles which can be components in subsea oil plumes. Certainchemicals can likewise effectively reduce the deleterious impact that anoil plume has on plant and animal life. The first step in developing aneffective response to oil spills, regardless of the cause, is knowingthe extent and location of the undersea oil plumes. Present technology,including sonar and turbidity measurements are fraught with problemsassociated with false positives and false negatives resulting from otherfactors present in the seawater. In many cases samples have to becaptured thousands of feet below the ocean's surface and physicallytaken to the ship where they can be investigated and characterized.

What is needed is an effective in situ system that effectivelyidentifies areas of hydrocarbon contamination in seawater by depth,location, concentration, and composition. By composition it isunderstood that effective responses rely on knowing the characteristicsof hydrocarbon, such as molecular weight and composition, which bemeaningful and sometimes critical in preparing an effective response toa hydrocarbons based environmental incident as well as the environmentalcondition in which the hydrocarbon is present, such as local salinityprofile, local sea water composition and presence, type andconcentration of surfactants.

What is desperately needed is a robust system that can effectivelydetermine both concentration of oil in seawater but also can providevaluable insights on the chemical properties of the oil, thus allowingfor a more effective, more focused and less costly response, all ofwhich can meaningfully preserve a delicate ecobalance and preserve theenvironment for generations to come. In addition, if it known where anoil plume is not, that information can allow officials to open areasthat fisherman and others rely on for their livelihoods. Such areasmight otherwise be closed to commercial fishers out of caution.

SUMMARY OF THE INVENTION

Described herein are systems, devices and methods for determining thecomponents of a fluid (or solution) using admittance spectroscopy. Inparticular, the devices, systems and methods described herein may beuseful for determining the identity, concentration, or identity andconcentration of one or more (or all) components of a fluid. Thesolution may be an aqueous solution (an aqueous fluid). In general, thecomponents of the fluid may be any compound, including (but not limitedto): ions, molecules, macromolecules, proteins, etc.

Because of the nature of the admittance spectroscopy systems, devicesand methods described herein, the identity and concentration of all ofthe components may be determined from the same admittance spectrographic“fingerprint.” The admittance fingerprint typically includes a pluralityof complex impedance measurements taken from a plurality of differentelectrodes exposed to the fluid, in which the surface interactionbetween the fluid and the various electrodes is different. The surfaceinteraction of different electrodes (or pairs of electrodes) will bedifferent, for example, if the surfaces are made of different materials,or have different geometries (including sizes, shapes, surfacestructures, microstructures, and material characteristics). Surfaces maybe coated, doped, processed, worked or otherwise treated to createdifferent surface interactions.

For example, described herein are methods of determining the identityand concentration of a compound or mixture of compounds in an solutionthat include the steps of: contacting a first surface with the solutionso that a boundary layer of solution is formed on the first surface;polling the first surface to determine the surface interaction betweenthe first surface and the compound or mixture of compounds in thesolution at the boundary layer; and determining the identity andconcentration of the one or more compounds based on the surfaceinteraction. The determination may be made with the aid of a storedlibrary of identified outputs, or a neural network based system whichcan identify compounds based on heuristics and learned values.

The method may also include the step of determining the identity andconcentration of the one or more compounds based on the surfaceinteraction and the bulk properties of the solution.

In some variations, the method includes the step of contacting a secondsurface with the solution. The surfaces (e.g., electrode surfaces) maybe immersed in the solution. For example, the step of contacting thefirst surface with the solution may comprise contacting the firstsurface in an aqueous solution.

The surface may be an electrode. For example, the first surface maycomprises a non-reactive surface of an electrode. The surface may becoated, treated, roughened, or the like. Surfaces may include boundactive (e.g., binding) agents (such as antibodies, charged elements,etc.).

The step of polling may include applying energy to determine the surfaceinteractions. Admittance spectroscopy applied at appropriate energy(e.g., typically low energy) may be used to poll or test the surfaceinteractions between the fluid and an electrode surface withoutdisturbing the equilibrium surface interactions. The surfaceinteractions between a particular electrode surface and a particularsolution at equilibrium are characteristic of the particular electrodesurface and the nature of the solution (e.g., the components in thesolution and, if applicable, the carrier solution). If the electrodesurface is a known, the (unknown) nature of the solution may bedetermined. For example, polling may comprise applying an electricalsignal to the first surface and measuring the complex admittance. Thus,the step of polling may comprise applying a plurality of electricalsignals and measuring the complex admittance at each signal. Inparticular, the polling step may be performed in a manner that preservesthe surface interaction between the solution and the electrode surface.For example, the step of polling may comprise applying an electricalsignal below the threshold for electrochemical reaction. The pollingstep may also be performed so that it does not disturb the dynamicequilibrium of the boundary layer on the first surface. For example, theenergy applied to poll the surface interaction may be below thethreshold for disrupting the surface interaction (e.g., within what isreferred to as the electrode polarization effect). In some variationsthis is between a threshold of approximately 0.5 V and 1 V.

In the determining step, it may be useful to compare the results of thepolling of surface with known surface interactions in order to identifythe components of the solution. Thus, it may be useful to poll multipledifferent surfaces (e.g., electrode surfaces) or to include additionalcharacteristic data, in addition to the surface interaction informationdetermined by polling. For example, the step of determining may comprisecomparing an indicator of surface interactions with a library of storedsurface interactions to determine concentration and identity of the oneor more compounds in the solution. The step of determining may comprisescomparing an indicator of surface interactions with a library of storedsurface interactions to determine concentration and identity of all ofthe compounds in the solution. In some variations, the step ofdetermining comprises simultaneously determining the identity andconcentration of the one or more compounds in the solution. Any of themethods described herein may also be used to determine both the identityand concentration. In some variations, the identity and concentrationmay be determined substantially simultaneously in the determining step.

Also described herein are methods of determining the identity,concentration, or identity and concentration of one or more compounds inan aqueous solution, the method comprising the steps of: placing a pairof electrodes in contact with the aqueous solution so that a boundarylayer of aqueous solution is formed on a first surface of one of theelectrodes; applying electrical excitation between the pair ofelectrodes to determine a complex admittance at the first surface,wherein the applied electrical excitation results in a voltage that isbelow the threshold level for electrochemical reactions at the firstsurface; and determining the identity, concentration, or identity andconcentration of one or more compounds in the aqueous solution based onthe complex admittance measured between the electrodes.

In some variations of the methods described herein, the method alsoincludes the steps of recording the complex admittance at a plurality ofcurrent frequencies. As already mentioned, the pair of electrodescomprises conductive surfaces made of different materials. The methodmay also include the step of placing a third electrode in contact withthe aqueous solution so that a boundary layer of aqueous solution isformed on a first surface of the third electrode, wherein the firstsurface of the third electrode is formed of a material that is differentfrom the material forming conductive surfaces on electrodes of the pairof electrodes.

The step of applying an electrical excitation may comprise applyingcurrent at a plurality of frequencies. In some variations, the step ofapplying an electrical excitation comprises applying electrical energyat a level that is below the thermal fluctuation energy in the fluid. Ingeneral, the step of applying electrical excitation may compriseapplying excitation a level that does not disturb the equilibrium of theboundary layer on the first surface.

Further, the step of determining may include comparing the complexadmittance with a library of complex admittance to determine identity,concentration, or identity and concentration of the one or morecompounds in the aqueous solution. The step of determining may includecomparing the complex admittance at different frequencies with a libraryof complex admittances to determine identity, concentration, or identityand concentration of the one or more compounds in the aqueous solution.The step of determining may comprise comparing the complex admittance atdifferent frequencies with a library of complex admittances to identityand concentration of the all of the compounds in the aqueous solution.

Also described herein are systems for determining the identity of asolution by admittance spectroscopy, the system comprising: a sensorcomprising a plurality of electrodes having fluid-contacting surfaces; asignal generator configured to provide electrical stimulation at aplurality of frequencies for application from the fluid-contactingsurfaces of the sensor; a processor configured to receive complexadmittance data from the sensor at the plurality of frequencies and todetermine the identity, concentration, or the identity and concentrationof one or more compounds in the solution by comparing the complexadmittance data to a library of predetermined complex admittance data.

In some variations, the fluid-contacting surfaces of the electrodes ofthe sensor are formed of a plurality of different materials, asmentioned above. The fluid-contacting surfaces of the electrodes of thesensor may be formed of a plurality of different geometries. In somevariations, the sensor comprises at least three differentfluid-contacting surfaces formed of different materials, different sizeor different materials and geometries.

The sensor may be configured as disposable (e.g., single-use) or it maybe reusable (e.g., washable). A plurality of sensors may be arranged asa strip, sheet, cartridge, etc., and the system or device may beconfigured to engage with one or more sensors either sequentially or inparallel (e.g., allowing parallel sampling of different solutions).

The fluid-contacting surfaces of the sensor may be calibrated to apredetermined standard that matches the predetermined complex admittancedata. For example, the sensors may include electrodes each having afluid-contacting surface that is calibrated to be within somepredetermined tolerances of geometry and materials forming the surface.The tolerances may be based on a standard (corresponding to the standardelectrode used to determine the library information). In some variationsthe system may verify that the electrode surfaces are within thetolerances. For example, the system may perform an initial check using astandard solution.

In some variations, the sensor comprises at least six independent pairsof fluid-contacting surfaces.

The system may include a signal receiver configured to receive complexadmittance data from the sensor and pass it on the processor. In somevariations, the system includes a measurement cell configured to receivethe solution so that the fluid-contacting surfaces of the sensor contactthe solution. The sensor may form a part (e.g., bottom, sides, etc.) ofthe measurement cell.

The signal generator may be configured to apply a current frequency fromabout 1 Hz to about 1 MHz. In some systems, configured for specificapplications the current frequency may range from about 5 Hz to about 50Hz. In other systems the current frequency may range from about 100 Hzto about 300 Hz. In other systems the current frequency may range fromabout 1 kHz to about 12 kHz in other system the current frequency mayrange from about 75 kHz to about 300 kHz, in other systems the currentfrequency may range from about 500 kHz to about 770 kHz. It has beenfound that the current frequency and current frequency range can resultin meaningful variations in application outcomes.

In some variations, the system includes a display configured to displaythe identity and concentration of the one or more compounds within thesolution. The processor may be further configured to determine theidentity of the carrier diluent. The carrier diluents may also bedisplayed.

The system may also include a controller configured to coordinateapplication of the signal from the signal generator and to acquisitionof complex admittance data from the sensor.

In general, the processor may include recognition logic configured todetermine the likeliest match between the complex admittance datareceived from the sensor and the library of predetermined complexadmittance data. The recognition logic may include an adaptive neuralnetwork trained on the library of predetermined complex admittance data.The library of predetermined complex admittance data may comprisecomplex admittance data measured for a plurality of individual compoundsand mixtures of compounds in a carrier diluent at a plurality offrequencies.

Any of the sensors described herein may also comprise an additionalsensor (or sensors), or sensor element, that is not a complex admittanceelectrode, and the processor may be configured to use data from thesecond sensor element in addition to the complex admittance data todetermine both the identity and the concentration one or more compoundsin solution. For example, the second sensor element may be an opticalsensor. In some variations, the system also includes a flow sensor, ormay be configured to receive information from a flow sensor.

The processor may be configured to receive complex admittance data fromthe sensor at the plurality of frequencies and to simultaneouslydetermine the identity and concentration of one or more compounds in thesolution by comparing the complex admittance data to a library ofpredetermined complex admittance data.

Also described herein are systems for determining the identity,concentration or identity and concentration of a solution by admittancespectroscopy that include: a sensor comprising a plurality of electrodeshaving fluid-contacting surfaces; a signal generator configured toprovide current at a plurality of frequencies for application from oneor more fluid-contacting surfaces of the sensor; a signal receiverconfigured to receive complex admittance data from one or morefluid-contacting surfaces of the sensor; a controller configured tocoordinate the application of signals from the signal generator and theacquisition of complex admittance data from the sensor to create anadmittance spectrographic fingerprint of the intravenous solution; and aprocessor configured to receive the admittance spectrographicfingerprint and to determine the identity, concentration or identity andconcentration of the intravenous solution by comparing the admittancespectrographic fingerprint to a library of admittance spectrographicdata comprising complex admittance data measured from a plurality ofknown compounds and mixtures of compounds in a carrier solution at aplurality of frequencies and known concentrations.

Also described herein are benchtop solution analyzers for determiningthe identity, concentration or identity and concentration of a solutionby admittance spectroscopy, the analyzer comprising: a measurement cellcomprising a plurality of electrodes having fluid-contacting surfaces,the measurement cell configured to receive a sample of the solution; asignal generator configured to provide electrical excitation at aplurality of frequencies for application from one or more pairs ofelectrodes of the measurement cell; a signal receiver configured toreceive complex admittance data from one or more pairs of electrodes ofthe measurement cell; a controller configured to coordinate theapplication of signals from the signal generator, and the acquisition ofcomplex admittance data from the signal receiver, to create anadmittance spectrographic fingerprint of the solution; and a processorconfigured to receive the admittance spectrographic fingerprint and todetermine the identity, concentration or identity and concentration ofone or more compounds in the solution by comparing the admittancespectrographic fingerprint to a library of admittance spectrographicdata comprising complex admittance data measured from a plurality ofknown compounds and mixtures of compounds in a carrier solution at aplurality of frequencies and known concentrations.

In some variations the analyzer includes a housing at least partiallyenclosing the signal generator, single receiver and controller. Theanalyzer may include a plurality of single-use measurement cells. Themeasurement cell may comprise at least three different fluid-contactingsurfaces formed of different materials, different geometries ordifferent materials and geometries. The fluid-contacting surfaces of themeasurement cell may be calibrated to a predetermined standard thatmatches complex admittance data of the library of admittancespectrographic data.

As mentioned above, the signal generator may be configured to apply acurrent frequency from about 1 Hz to about 1 MHz.

The analyzer may include a display configured to display the identityand concentration of the one or more compounds within the solution.

The processor be any of the processors described above. For example, theprocessor may be further configured to determine the identity of thecarrier solution of the solution, and the library of predeterminedcomplex admittance data used by the processor may include complexadmittance data measured for a plurality of individual compounds andmixtures of compounds in a carrier solution at a plurality offrequencies.

The measurement cell may further comprise a second sensor element, andthe processor may be configured to use data from the second sensorelement in addition to the admittance spectrographic fingerprint todetermine both the identity and the concentration of one or morecompounds in the solution. The second sensor element may comprise anoptical sensor.

In some variations, the processor is configured to receive theadmittance spectrographic fingerprint and to simultaneously determinethe identity and concentration of one or more compounds in the solution.

Also described herein are systems for controlling the delivery of afluid by determining the identity, concentration or identity andconcentration of one or more components of the intravenous fluid usingadmittance spectroscopy. The system may include: a sensor having aplurality of complex admittance electrodes configured to contact afluid; a signal generator configured to provide electrical excitation ata plurality of frequencies for application across the plurality ofcomplex admittance electrodes; a processor configured to receive complexadmittance data from the sensor at the plurality of frequencies and todetermine the identity, concentration or the identity and theconcentration of one or more compounds in the intravenous fluid bycomparing the complex admittance data to a library of predeterminedcomplex admittance data; and a control output configured to regulate theoperation of a delivery device based on the determined identity,concentration or concentration and identity of one or more compounds inthe intravenous fluid.

The intravenous delivery device may be any appropriate delivery system.For example, the intravenous delivery device may be a pump. The pump maybe a “smart pump” that includes electronic control of pump rate, and thelike. The control output may be configured to modulate, adjust, turn offor suspend delivery of the intravenous delivery device.

The processor may be configured to receive flow information from a flowsensor in communication with the intravenous fluid and to determine adelivered dose of the one or more compounds in the intravenous fluid. Insome variations, the sensor further comprises a flow sensor.

The processor may be configured to simultaneously determine the identityand the concentration of one or more compounds in the intravenous fluid.

Also described herein are methods of determining the identity andconcentrations of one or more compounds in a solution by admittancespectroscopy, the method comprising: applying electrical excitation at aplurality of frequencies between at least one pair of fluid-contactingsurfaces in contact with the solution; determining the complexadmittance between at least one pair of fluid-contacting surfaces at theplurality of frequencies; creating an admittance spectrographicfingerprint of the solution comprising the complex admittance from theat least one pair of fluid-contacting surfaces at the plurality offrequencies; and determining both the identity and the concentration oneor more compounds in the solution by comparing the admittancespectrographic fingerprint to a library of admittance spectrographicdata comprising complex admittance data measured from a plurality ofknown compounds and mixtures of compounds in a carrier solution at aplurality of frequencies and known concentrations.

As mentioned, the solution may be a solution, a parenteral solution, aparenteral solution, or the like. The method may also includedetermining the identity and concentration of all of the components ofthe solution.

Also described herein are methods of determining the identity andconcentrations of one or more compounds in a solution by admittancespectroscopy, the method comprising: applying electrical excitation at aplurality of frequencies between two or more pairs of fluid-contactingsurfaces in contact with the solution, wherein at least one of the fluidcontacting surfaces is formed of a different material, different size,or different material and size than the other fluid contacting surfaces;determining the complex admittance from the two or more pairs offluid-contacting surfaces at the plurality of frequencies; creating anadmittance spectrographic fingerprint of the solution comprising thecomplex admittance from the two or more pairs of fluid-contactingsurfaces at the plurality of frequencies; and determining both theidentity and the concentration one or more compounds in the solution bycomparing the admittance spectrographic fingerprint to a library ofadmittance spectrographic data comprising complex admittance datameasured from a plurality of known compounds and mixtures of compoundsin a carrier solution at a plurality of frequencies and knownconcentrations.

Also described herein are methods of simultaneously verifying both thecomposition and concentration of a solution, the method comprising:preparing the intravenous solution; testing a sample of the intravenoussolution and independently and simultaneously determining both theidentity and concentration of one or more components of the intravenoussolution.

The step of testing may include determining an admittance spectrographicfingerprint comprising a plurality of complex admittances taken atdifferent frequencies. In some variations, the step of testing comprisesdetermining an admittance spectrographic fingerprint comprising aplurality of complex admittances taken at different frequencies andcomparing the admittance spectrographic fingerprint to a library ofadmittance spectrographic data comprising complex admittance datameasured from a plurality of known compounds and mixtures of compoundsin a carrier solution at a plurality of frequencies and knownconcentrations.

Water condition monitoring for quality and/or contamination. Oneembodiment provides a multi-parametric measurement system that includesmulti-electrode impedance spectroscopy either alone or in conjunctionwith other measurement techniques can be utilized to detect, quantify,monitor or control the levels of contaminants, mineral content,chlorination levels, etc in water. Examples can include but are notlimited to applications such as monitoring of water purificationsystems, control of pool chemical levels, waste treatment effluentmonitoring and monitoring streams, rivers, bays, and oceans forcontamination such as pesticides, fertilizers or industrial runoff

Another embodiment provides measurement of oil and detergent dispersedin water, especially seawater. A multi-parametric measurement systemthat includes multi-electrode impedance spectroscopy either alone or inconjunction with other measurement techniques can be utilized to detectand quantify dispersed oil in water including cases in which dispersantsor detergents have been utilized to break down oil spills and dispersethem into water.

Another embodiment provides measurement of urea concentration in waterfor diesel engine NOx reduction systems. A multi-parametric measurementsystem that includes multi-electrode impedance spectroscopy either aloneor in conjunction with other measurement techniques can be utilized todetect, quantify, monitor or control the levels of urea in water usedfor nitrous oxide (NOx) in diesel engine systems. Such a system canensure the urea is at proper concentration and has not been contaminatedor replaced with foreign substances such as salt, sugar, etc.

In another embodiment the invention provides for monitoring and closedloop control of food and chemical manufacturing processes. Amulti-parametric measurement system that includes multi-electrodeimpedance spectroscopy either alone or in conjunction with othermeasurement techniques can be utilized to monitor and control chemicalmanufacturing processes. Examples can include the production ofherbicides, pesticides, industrial chemicals, drugs, cosmetics fermentedalcohol products, distilled alcohol products and foods

In another embodiment the invention provides for down hole oil wellmeasurements to determine water, saline, methane, oil content etc. Amulti-parametric measurement system that includes multi-electrodeimpedance spectroscopy either alone or in conjunction with othermeasurement techniques can be utilized for oil well logging or drillingmonitoring to determine the makeup of the fluid in an oil well includingdrilling muds.

In addition, the technology described herein can be applied either as amonitor or control device to a wide range of process and quality controlapplications in chemical manufacturing and use, fuel refining anddelivery, food manufacturing, semiconductor manufacturing and industrialprocesses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an admittance spectrographic system fordetermining the composition of a fluid.

FIG. 2 illustrates the formation of an electrical double layer onfluid-contacting surface of an electrode, illustrating the dynamicequilibrium of the solution components on the surface.

FIG. 3 is the equivalent circuit for the electrode-solution interfaceshown in FIG. 2.

FIG. 4 is a graph showing the electrode polarization effect (adaptedfrom Walton C, Gergely S, Economides AP. Platinum pacemaker electrodes:origins and effects of the electrode-tissue interface impedance. PacingClin. Electrophysiol. 1987; 10:87-99).

FIG. 5 schematically illustrates one variation of an admittancespectrographic system for determining the composition of a fluid.

FIG. 6 schematically illustrates another variation of an admittancespectrographic system for determining the composition of a fluid.

FIG. 7A is a schematic of a modified Scitec Instruments model 441 boardlevel lock-in amplifier.

FIG. 7B shows a block diagram for a Scitec #441 Lock-in amplifer.

FIG. 8 schematically illustrates another variatoin of an admittancespectrographic system for determining the composition of a fluid.

FIG. 13A is one variation of a sensor having six complex admittanceelectrodes arranged thereon.

FIG. 13B is another variation of a sensor including six complexadmittance electrodes (similar to those shown in FIG. 13A), and a flowsensor (thermal anemometer flow sensor) and an optical waveguide.

FIG. 13C is a miniaturized version of the sensor of FIG. 13B.

FIG. 13D is a blow-up of the flowmeter traces of the sensor on FIG. 13Band FIG. 13C.

FIG. 14 is a panel of sensors similar to those shown in FIG. 13B thatmay be manufactured using metal deposition and lithography.

FIGS. 15A and 15B shows integration of complex admittance sensor withthe multi-wavelength optical sensor

FIG. 16 illustrates one variation of a thermal anemometer flow sensor.

illustrate schematics of two variations of a data structure representingan admittance spectrographic footprint.

FIGS. 19A through 19L show complex admittance sensor patterns for 3different metals and 3 different metal combinations in various samplesof water from different sources including marine water samplescontaminated by oil and detergent.

DETAILED DESCRIPTION OF THE INVENTION

Described herein are devices, systems, and methods for determining thecomposition of fluids. The composition typically includes both identityand concentration, and may include the determination of all of thecomponents of the fluid. Many of the devices, systems and methodsdescribed herein may allow for essentially simultaneous determination ofthe concentration and/or identity of all of the components in the fluid.In particular, the systems, methods and devices described herein areadmittance spectrographic systems, methods and devices which determinethe complex electrical admittance of the fluid under multiple surfaceconditions (either sequentially or in parallel) and/or at multipleapplied frequencies in order to determine characteristic properties thatmay be used to determine identity and concentration. In some variations,additional measurement or sensing modalities may be used in addition toadmittance spectroscopy, including optical, thermal, chemical, etc.

A fluid admittance measurement typically involves the measurement of thereal and imaginary components a of the alternating current (ac) responseof a fluid to applied electrical current at a particular frequency, setof frequencies or within a range of frequencies. These components arealso sometimes referred to as the in-phase and quadrature or theresistive and reactive components of an ac response. This technique isherein demonstrated for the identification of fluids, components influids, and particularly to the identification of compounds such ashydrocarbon containing compounds found in seawater.

FIG. 1 shows a generic description of a system or device for determiningthe composition of an aqueous solution. In general, the system or devicemay include a plurality of electrodes (105, 105′, . . . , 105″), eachhaving a fluid-contacting region (103, 103′, . . . , 103″). At leastsome of the electrodes may have different fluid-contacting surfaces. Asdescribed in greater detail below, the complex admittance determinedacross individual pairs of electrodes may depend upon the interaction ofthe aqueous solution and the components within the solution at thesurface of the electrode (the fluid-contacting surface). Thus, thesurface properties (including the size and materials forming thesurface) may be controlled and matched to known or standardizedfluid-contacting regions of the electrodes. Typically each electrodepair may have at least one fluid-contacting surface that is differentfrom fluid-contacting surfaces in other pairs, in variations of thesystems in which multiple electrode pairs are used. The electrodes maybe formed as part of a probe 107, test cell or test chamber, tubing, ormay be integrated into another device, such as a pump or the like.

The system or device may also include a signal generator 121 forapplying an electrical signal across one or more pairs of theelectrodes, and a signal receiver 131 for receiving an electrical signalrepresenting the complex admittance. The signal receiver may includeprocessing (amplification, filtering, or the like). The system mayinclude a controller 119 for coordinating the application of theelectrical signal to the one or more pairs of electrodes, and forreceiving the complex admittance data. For example, a controller mayinclude a trigger, clock or other timing mechanisms for coordinating theapplication of energy to the electrodes and receiving complex admittancedata. The system or device, including a controller 119, may also includea memory for recording/storing the complex admittance data. The systemor device also typically includes a processor 131 for analyzing thecomplex admittance data to determine the identity and concentration ofthe components of the aqueous solution based on the complex admittancedata. Details and examples of the processor are described in greaterdetail below. In general, the processor may include logic (executable ashardware, software, firmware, or the like) that compares all or a subsetof the received admittance data (forming an “admittance spectrographicfingerprint”) to a database (e.g., library) of spectrographic datacorresponding to known fluid compositions, at known components andconcentrations. The processor may interpolate recognition logicconfigured to determine the likeliest match between the admittancespectrographic fingerprint and this known admittance spectrographicdata. The processor may also use other information in conjunction withor in addition to the admittance data. For example, the system mayinclude one or more sensors for determining other properties of thefluid, including characteristic properties that may help identify one ormore components of the fluid (e.g., optical information). The processormay use this additional data to help identify the composition of thefluid. In other variations, the processor may receive information fromsensors that determine fluid properties that may also be used to helpcharacterize the administration of the fluid, or the operation of otherdevices associated with the fluid. For example, a flow sensor may beincluded as part of the system; the processor may also be configured todetermine or receive flow information, and may calculate the total orinstantaneous dosage of one or more components of the fluid.

Finally, a general device or system may include an output 141 forreporting, recording and/or acting on the identified composition of theaqueous solution. The output may be visual, audible, printed, digital,or any other appropriate output. In some variations described herein,the system or device may regulate or modify activity of one or moredevices associated with the fluid or with a process receiving fluid,such as industrial process, marine engine cooling system, etc. Forexample, a system may turn off or limit delivery of a substance bycontrolling operation of a fluid pump based on the analysis of thecomposition of the fluid.

A system or device for determining the composition of an aqueoussolution as described herein may be particularly useful forenvironmental applications, though not strictly limited to suchapplications. Thus, in many of the examples and variations describedherein the devices and systems are for analyzing, monitoring or testingseawater. Both in-situ and benchtop systems are described. Integratedsystems, in which the devices/systems for determining composition of theaqueous solutions are connected or integral to other devices or systemsare also contemplated and described.

In many of the admittance spectroscopy systems and devices describedherein, multiple polarizable electrodes consisting of electrode pairs ofidentical and different materials are utilized. As mentioned, in somevariations, multiple electrode admittance spectroscopy is used andeither applied alone or in conjunction with otheridentification/characterization sensors and methods, including opticalsensors. Examples of electrodes either alone or with additional sensorsin variations configurations of probes and measurement cells includingelectrodes (and particularly electrodes having fluid-contacting regions)are described in greater detail below.

Examples of various systems are also described. Although many of thesesystems may include just admittance spectroscopy, the examples describedherein often include additional sensors. For example, a systemincorporating automated computer control for measurement of fluidadmittance over a range of frequencies and using a set of multipledifferent electrodes has been developed. This system includes a sensorelement consisting of a set of electrodes coupled to a measurementsystem and computer for data acquisition and system control. It alsoincludes 4 optical sources and detectors at specific wavelengths. It isto be understood that these systems do not require the use of theadditional (e.g., optical) sensing modality, and may be constructed andused with just the admittance spectroscopy features.

Admittance Spectroscopy

PCT patent application PCT/US2009/001494 incorporated by reference abovedescribes the application of multiple parameters (including multiplesensors) that each provide different characteristics which may becombined to create a multiparametric fingerprint of a solution. Thismultiparametric technique (and embodiments thereof) may be used in anenvironmental setting to locate and identify the size, location andcomposition of an undersea hydrocarbon plume. Described herein aresystems and devices that may also be considered multiparametric, inwhich the “fingerprint” that is taken from the solution in order todetermine the composition of the solution includes admittancespectroscopy information taken from the solution.

Thus, in the context of the present disclosure, a multiparametricfingerprint of a solution will include a plurality of admittancespectrographic data. The “fingerprint” may therefore be referred to asan admittance spectrographic fingerprint, although additionalidentifying information may be included, as described in greater detailbelow (such as optical, thermal, etc.). The fingerprint may be collectedor compiled as a matrix or array of values, and it may be plotted,graphed, mapped, or the like. In some variations, the fingerprint mayinclude time-varying data, and may be indexed by a temporal and/orspatial element (e.g., at points taken over time, or taken after sometriggering event). The parameter values forming the multiparametricfingerprint may be indexed by the sensor (e.g., electrodes) thatacquired them. The fingerprint may include at least two dimensions (suchas real and complex impedance) and may include many more than twodimensions (e.g., real and complex impedance at a plurality offrequencies, or real and complex impedances for multiple electrode pairshaving different surface interactions with the fluid at differentfrequencies). The parameter values within the fingerprint (e.g., thecomplex impedance values) may be averages, medians, or means. In somevariations the values forming the fingerprint may be filtered. In somevariations the values forming the fingerprints are normalized. In somevariations, the information forming the fingerprint is derived fromcombined (e.g., subtracted, added, scaled, etc.) data.

The admittance spectrographic fingerprint described herein may becompared, as described herein, in order to determine the composition ofthe fluid, which may include simultaneously determining the identity andconcentration of all components in the solution, including the identityof the carrier solution. Thus, in some variations, the acquired(unknown)) fingerprint may be compared against known fingerprints thatmay be included in a library of fingerprints provided for known solutioncompositions.

The electrodes used to measure complex admittance described herein aretypically made of metals that are non-reactive with the components ofthe fluids that they contact, and generally, ions of the utilized metalsare not materially present in the sensed fluids. This allows thedetermination of the characteristic steady-state complex impedance.However, it has long been known that such electrodes, when exposed to anaqueous solution such as seawater, exhibit so-called “blocking”behavior: a DC voltage applied to such metal electrode results in zeronet charge transfer through metal-electrolyte interface unless thevoltage exceeds certain level. This effect is called electrodepolarization and has been studied since 1879 (see, e.g., Helmholtz H.Studien ëber electrische Grenzschichten. Annalen der Physik and Chemie.1879; 243(7):337-382, or the translated version: “Studies of electricboundary layers”. translated by P. E. Bocque, Bull. Dep. EngineeringResearch Univ. Mich. 33, 5-47 (1951)).

Electrode polarization is particularly well-researched and documented inthe field of implantable electrodes for pacemakers, where the presenceof this effect impedes efficient cardiac activity sensing andstimulation. For example, when a platinum pacemaker electrode isimmersed in a bath of physiological saline and a DC voltage is appliedto it within a range of potentials, virtually no current flows throughthe electrolyte unless the voltage exceeds values of approximately ±1 V.Below this voltage the electrodes demonstrate capacitive behavior. Thiseffect is illustrated in FIG. 4. To achieve successful pacing with thelimited available electrode area, pacemakers typically rely on chemicalreactions at the electrode interface to pass sufficient charge to thetissue, and overcome this electrode polarization effect. See, e.g.,Walton C, Gergely S, Economides AP. Platinum pacemaker electrodes:origins and effects of the electrode-tissue interface impedance. PacingClin. Electrophysiol. 1987; 10:87-99).

The complex admittance measured from a particular fluid-contactingsurface reflects the interaction of the solution and any compounds inthe solution and the surface of the fluid-contacting surface. Theinteraction between the fluid-contacting surface and the fluid (at theinterface) may be established shortly (if not virtually immediately)upon contacting the fluid to the surface. The surface may be probed (bythe application of electrical energy) to determine the compleximpedance, and the complex impedance is characteristic of theinteraction between the fluid and the fluid-contacting surface of theelectrode. Thus, the complex impedance determined at a particularsurface reflects the nature of the interaction between thefluid-contacting surface and the solution, and may therefore depend onthe material forming the fluid-contacting surface and the geometry ofthe fluid contacting surface (e.g., the surface area). Differentsurfaces may produce different complex impedances in the same solution,because the interactions with the fluid may differ between differentfluid-contacting surfaces (including the sizes, and the materialsforming the fluid-contacting surfaces). As used herein the termfluid-contacting surface typically refers to the conductive(non-insulated) region of an electrode that contacts the fluid. Thefluid contacting surface may include a coating or the like, and may besurrounded by an insulating region. For example, the complex impedanceof a silver-silver electrode pair may be very different than the compleximpedance of a silver-gold electrode pair with the same geometrymeasured in the same solution at the same frequency and current level.

Because the complex admittance is so variable and sensitive to thecomposition (and geometry) of the fluid-contacting surface of theelectrodes, particularly when probed at low power levels (e.g., currentand/or voltage levels), complex impedance has not previously beensuccessfully used as a method for determining the composition of anunknown aqueous solution.

Admittance spectroscopy may also be referred to as immittancespectroscopy (impedance or admittance), which encompasses a variety oftechniques for the measurement and analysis of the complex impedance(Z), the complex admittance a % and the complex dielectric constant (∈)as a function of frequency. These values may be plotted in the complexplane. The complex plane is typically defined as standard orthogonal xyframe of reference in which the complex impedance (Z=Z′+iZ″), admittance(Y=Y′+iY”), and/or dielectric constant (∈=∈′+i∈″) is plotted so thatx=Z′, y=Z″; x=Y′, y=Y″; x=∈′, y=∈″, where ′ and ″ are real andquadrature components of the complex value.

When a solution first contacts a surface such as an electrode surface,the surface interaction between the electrode and the fluid results inthe formation of a layered boundary as illustrated in FIG. 2. Thislayered boundary may be characteristic of the electrode surface and thesolution, and may be dependent upon the composition of the solution aswell as the composition and/or structure of the surface. In general,multiple “layers” are formed between the surface and the solutionforming an interface of sorts. For example, in FIG. 2, three differentregions may be formed between the surface of the electrode and the bulkof the fluid: the IHP (inner Helmholtz plane) is closest to the surface,the OHP (outer Helmholtz plane) is the next layer, followed by a diffuselayer that gradually transitions to the bulk solution.

In many of the variations described herein, the electrodes are fullypolarizable electrodes, in which no charge transfer is possible at lowpotentials (voltages), e.g., below some Φ_(i), which is typically atleast 500 mV, and thus electro-chemical reactions will not take place atthe electrode surface. If the excitation voltage ΔV does not disturb thesystem much more that naturally occurring thermal fluctuations, then theresponse to the applied current is linear, so that: ΔV˜kT/e, where k isBoltzmann's constant, T is absolute temperature and e is the electroncharge. ΔV is approximately 25 mV at room temperature.

Thus, at the surface of an electrode, the complex AC impedance Z(ω) oradmittance Y(ω) can be approximated as an equivalent circuit shown inFIG. 3, and can be measured. The relationship for impedance can beexpressed as:

$\begin{matrix}{{Z(\omega)} = {{Z^{\prime}(\omega)} + {\; Z^{{\prime\prime}{(\omega)}}}}} \\{= {\left( {R_{2} + \frac{R_{1}}{1 + \left( {\omega \; C_{2}R_{1}} \right)^{2}}} \right) -}} \\{{\left( {\frac{1}{\omega \; C_{1}} + \frac{\omega \; C_{2}R_{1}^{2}}{1 + \left( {\omega \; C_{2}R_{1}} \right)^{2}}} \right)}}\end{matrix}$

The equivalent circuit resulting from this model of themetal-electrolyte interface contains 4 independent parameters (R₁, R₂,C₁, C₂) that are affected by the presence of any compounds in thesolution, for example, surfactant and hydrocarbon content in anartificial seawater (ASW) or other standard or representative referencesolution. The individual components of the equivalent circuit are notdirectly accessible in practice, but can be measured indirectly throughmeasurements of the cell's time-dependent response to excitation currentor voltage or through AC impedance or admittance. It may be morestraightforward to measure AC current rather than impedance and workwith admittance, although it leads to bulkier formulae, for example:

${Y(\omega)} = {\frac{\left( {\omega \; C_{1}} \right)^{2}\left( {R_{1} + {R_{2}\left( {1 + \left( {\omega \; C_{2}R_{1}} \right)^{2}} \right)}} \right)}{\left( {{\omega \; C_{2}R_{1}} + {\omega \; {C_{1}\left( {R_{1} + R_{2}} \right)}}} \right)^{2} + \left( {{\omega \; C_{1}\omega \; C_{2}R_{1}R_{2}} - 1} \right)^{2}} + {\; \frac{\omega \; C_{1}\left( {1 + {\omega \; C_{1}\omega \; C_{2}R_{1}^{2}} + \left( {\omega \; C_{2}R_{1}} \right)^{2}} \right)}{\left( {{\omega \; C_{2}R_{1}} + {\omega \; {C_{1}\left( {R_{1} + R_{2}} \right)}}} \right)^{2} + \left( {{\omega \; C_{1}\omega \; C_{2}R_{1}R_{2}} - 1} \right)^{2}}}}$

The values of the 4 independent parameters can be calculated from twomeasurements of impedance or admittance at two different frequencies ω₁and ω₂. If complex impedance is measured: Z₁=Z(ω_(i))=a₁+ib₁ andZ₂=a₂+ib₂ the equivalent circuit parameters are calculated as follows:

$C_{1} = \frac{\left( {{\omega_{1}b_{1}} - {\omega_{2}b_{2}}} \right)\left( {\omega_{1}^{2} - \omega_{2}^{2}} \right)}{\omega_{1}{\omega_{2}\left( {{\omega_{1}{\omega_{2}\left( {\left( {a_{1} - a_{2}} \right)^{2} + b_{1}^{2} + b_{2}^{2}} \right)}} - {b_{1}{b_{2}\left( {\omega_{1}^{2} + \omega_{2}^{2}} \right)}}} \right)}}$$R_{1} = {- \frac{\left( {a_{1} - a_{2}} \right)^{2}\left( {{\omega_{1}b_{1}} - {\omega_{2}b_{2}}} \right)^{2}}{\left( {a_{1} - a_{2}} \right)\left( {{\omega_{1}b_{1}} - {\omega_{2}b_{2}}} \right)^{2}\left( {\omega_{1}^{2} - \omega_{2}^{2}} \right)}}$$C_{2} = \frac{\left( {a_{1} - a_{2}} \right)^{2}\left( {{\omega_{1}b_{1}} - {\omega_{2}b_{2}}} \right)\left( {\omega_{1}^{2} - \omega_{2}^{2}} \right)}{\begin{matrix}\left( {{\omega_{1}^{2}\left( {a_{1} - a_{2}} \right)}^{2} + \left( {{\omega_{1}b_{1}} - {\omega_{2}b_{2}}} \right)^{2}} \right) \\\left( {{\omega_{1}^{2}b_{1}^{2}} - {2\omega_{1}b_{1}\omega_{2}b_{2}} + {\omega_{2}^{2}\left( {a_{1} - a_{2}} \right)}^{2}} \right)\end{matrix}}$ $R_{2} = \frac{\begin{matrix}{{\omega_{1}^{2}\left( {a_{1}^{2} + b_{1}^{2}} \right)} - {2\omega_{1}\omega_{2}b_{1}b_{2}} +} \\{{\omega_{2}^{2}\left( {a_{2}^{2} + b_{2}^{2}} \right)} - {a_{1}{a_{2}\left( {\omega_{1}^{2} + \omega_{2}^{2}} \right)}}}\end{matrix}}{\left( {a_{1} - a_{2}} \right)\left( {\omega_{1}^{2} - \omega_{2}^{2}} \right)}$

These four independent parameters may be used to determine the compleximpedance, and for angle calculations and clustering for substancerecognition as described below. Multiple measurements at one or eachfrequency can be made to average signal and improve signal to noiseratio (SNR). More than 2 measurements at 2 different frequencies can beused to calculate the above four parameters. Multiple frequencymeasurements may provide the redundancy in data that can be utilized toimprove SNR though known algorithms such as least squares method.Although the measurements described above reference frequency domainmeasurements, the equivalent information can be obtained from timedomain measurements.

However, when determining the complex admittance of a solution, it isoften desirable to use an excitation energy as low as possible, toprevent electrochemical reactions at the surface of the electrode whichmay both prevent a stable determination the complex admittance, and mayundesirably modify or effect the solution being tested. Thus, in thevariations described herein, the excitation energy applied between thesensor electrodes is typically kept below the threshold voltage of anyelectrochemical reactions that may occur in the fluid. Preferably, theexcitation energy applied between the sensor electrodes is kept belowthe characteristic value of the energy associated with the naturallyoccurring thermal fluctuations.

Thus, sensors described herein typically operates at voltagesignificantly lower than the threshold necessary to avoid the electrodepolarization effect, in order to avoid triggering electrochemicalreactions at the electrode-fluid interface. The threshold is typicallybetween about 0.5V and about 1 V (e.g., about 0.5V, 0.6V, 0.7V, 0.8V,0.9V, and 1.0V). Based on our preliminary work, we have determined that,the typically undesirable electrode polarization effect may in factprovide useful information and important information regarding thenature and condition of the electrode-fluid interface. For the responseto be described in terms of the cell AC admittance, all of themeasurements should be performed within the voltage range where currentis proportional to voltage—linear regime. This regime is well covered inpacemaker-related studies, where the electrode polarization effect isconsidered problematic. Electrode polarization is considered a majorsource of effort in determining the impedance of biological samples insolution (see, e.g., Oh et al., “Minimization of electrode polarizationeffect by nanogap electrodes for biosensor applications” Porc. MEMS-03Kyoto Micro electro mechanical Systems IEEE The Sixteenth AnnualInternational Conference on, pages 52-55, Jan. 19-23, 2003).

The application of energy above the threshold in order to overcome thepolarization effect (e.g., above 1 V) typically results in an externalelectric field strong enough to disturb the natural arrangement of fluidcomponents within the double layer adjacent to the electrode surface andmay result in electrochemical reactions. The structure of the fluidlayers adjacent to the electrode interface is not static, but ratherexists in dynamic equilibrium under naturally occurring thermalfluctuation. The fluctuating energy associated with thermal motion of anionic media can be estimated as kT/e, where k is Boltzmann's constant, Tis absolute temperature in K° and e is electron charge, which at roomtemperature is about 25 mV.

The complex admittance sensors described herein typically operate atexcitation voltage of approximately 30 mV amplitude (˜21.2 mV RMS),which is of the same magnitude as the voltage associated with naturalthermal fluctuation. This operation regime ensures that sensor measuresresponse of the fluid cell without considerable disturbance of theelectrode/fluid interface, and allows the unexpected advantages ofoperating within the regime of electrode polarization which waspreviously avoided.

By exploiting the usually undesirable electrode polarization effect, thedevices and systems described herein may probe the dynamic equilibriumformed at the interface of the electrode and the fluid being testedwithout disturbing this naturally occurring fluid stratification. Sincethe equilibrium is rapidly formed, and is characteristic of the fluid,this information may provide information about the interface between theknown surface of the electrode and the unknown fluid being tested. Inoperation, the devices and systems may therefore use multiple, differentelectrodes (e.g., electrodes having different surface interactions withthe solution being tested). These electrodes used to generate theadmittance spectra are typically polarizable, and the system is operatedbelow the thermal energy of the sample. This may allow for multiple,highly reproducible measurements to provide signatures based on thecomplex admittance that depend on the composition and concentration ofcomponents in the solution.

Benchtop System or Device

Some variations of the devices and systems described herein areconfigured to be used to test solutions that are not typically flowing.For example, a system may be configured to test collected mixtures ofaqueous solutions. These systems may therefore be referred to as abenchtop device or system. For example, a benchtop system may be used toby scientists to validate movement or presence of an oil plume when itis impractical to deploy a sufficient number of sensors.

Benchtop device typically includes a measurement cell or chamber intowhich a sample of the solution to be tested is applied. For example, insome variations the system will have a sensor chamber that could be inthe form of an optical cell in which the sensor element is molded orinserted. A sample to be tested is introduced into the cell and itselectrical (and in some variations also other properties) may bemeasured to generate a set of 3 or more independent measurement values.These values in aggregate will create a means of identifying aparticular substance from another, which may be the admittancespectrographic fingerprint of the sample. The values of each of themultiple data channels, when combined, can produce a unique pattern foreach compound it measures and thus provide a means of identifying fluidcomponents.

In one example of a benchtop system described herein, the system (ordevice) includes a measurement sensor that is part of a measurementcell, and that is utilized in conjunction with a lock-in amplifier thatsupplies excitation signals and detects the resulting signals reflectingthe complex admittance at different frequencies. A controller (e.g., acomputer system, dedicated processor, or the like) may control thesignals and acquire the data.

For example, FIG. 5 shows a diagram of one variation of a benchtopsystem. In this example, the system includes a sensor element (typicallyhaving multiple electrodes), a lock-in amplifier for application andreceiving signals to/from the electrodes, and a control and dataacquisition system to control the application of energy and therecording of complex admittance.

This benchtop system implements multiple electrode fluid admittancemeasurements. In some variations, the system may also implementadditional (non-admittance) sensors. For example, optical sensors (e.g.,measuring multiple wavelength refractive index and absorptionmeasurements), as discussed in greater detail below.

FIG. 6 shows a slightly more detailed schematic of a benchtop system,configured to measure both complex admittance and optical sensorelements. This system includes a control and acquisition sub-system 601(e.g., National Instruments sbRIO 9632) that may include analog todigital and digital to analog circuitry for generating and detectingsignals, as well as a field programmable gate array (FPGA) and on boardmicroprocessor with an embedded real-time operating system. This mayalso provide over 100 digital lines, some of which may be used forcontrol and switching applications in the device.

In this example, a modified Scitec Instruments model 441 board levellock-in amplifier 603 (a schematic of which is shown in FIG. 7A) is usedfor signal detection. A programmable excitation signal source 605 wasbuilt by modifying an AD9951 DDS VFO board kit obtained from HagertyRadio. The system also includes a sensor element 609 which is part of ameasurement cell 611, utilized in conjunction with a switching system613 to enable automated measurement of the signal from all combinationsof the 6 elements on the sensor chip and all 4 optical measurementchannels. This switching sub-system 613 may be computer controlled.

The exemplary prototype shown in FIG. 6 allows testing and switching ofmultiple admittance electrodes and optical sensor channels. Thisswitching allows the system to take a plurality of complex admittancemeasurements (often simultaneously), and to store this data along withthe additional (optional) optical data and construct an admittancespectroscopy fingerprint that is characterisitc of the composition ofthe fluid. Although any approriate synchronous detector or other lock-inamplifier may be used, FIGS. 7A and 7B illustrate board layout and blockdiagrams for the Scitec #441 Lock-in amplifer example described above.

Another example of a benchtop variation of the devices and systems fordetermining the composition of a fluid is shown in FIG. 8. In thisexample, a sensor 801 may be part of a measurement cell (not shown), andit may be a reusable sensor or a disposable/single use sensor. Thesensor may be embedded (or may form part of) the measurement cell, or itmay be inserted into the measurement cell. In this example the sensor801 includes six electrodes which may form up to 15 different channelsfor independently sampling complex admittance, if each electrode has adistinct surface interaction with the sample fluid. In FIG. 8, threedifferent electrodes are used (e.g., Au, Au, Pd, Pd, Ti, Ti) forming sixunique electrode pairs (Au—Au, Au—Pd, Au—Ti, Pd—Pd, Pd—Ti, Ti—Ti), and aswitch matrix 803 is used to control which electrodes are active forprobing by applying energy and determining the resulting complexadimttance. A programmable (and controllable) excitation source 805drives excitation of the electrode pairs, and a signal receivingsub-system, including signal conditioning circuit 807 is used as well.The signal conditioning circuit 807 may be used to smooth, filter,amplify, or otherwise modify the signal. The receiving sub-system mayalso include a lock-in amplifier 809. A controller 811 may control theexitation and data collection, including regulating, synchronizing,and/or triggering the system and may also collect, pass on, and/or storethe data.

The system in FIG. 8 includes a wireless output that may communicatewith one or more computers 813 or other targets. However, anyappropriate target may be used. In addition, the processor that isconfigured to analyze the received admittance spectroscopic informationmay be a dedicated processor, or it may include software, hardwareand/or firmware running on a dedicated or general-purpose computer. Insome variations the processor is directly coupled to the rest of thesystem. In FIG. 8, the processor may be integrated into the controller811, or it may be part of the computer 813 to which the systemwirelessly communicates.

FIG. 9 shows a prototype of a benchtop system, including a test cellregion 903, into which a sample of fluid may be loaded. A sensor wasformed by lithographic techniques, as described below, forming sixunique pairs of electrodes: Au—Au, Au—Pd, Au—Ti, Pd—Pd, Pd—Ti, andTi—Ti. In practice, any of these electrodes or pairs of these electrodescan be used for either excitation and/or reception (e.g., excitationpair: Au—Pd, reception: Ti, or excitation: Au, reception: Pd—Ti, etc).

In FIG. 9, the device also includes a controller housing 905, which maycontain the signal generator/excitation source, and signal receiverelements for detecting the complex admittance. A processor for analyzingthe admittance fingerprint may also be included within the housing. Inthis example, the benchtop device is approximately the size of anotebook computer, and uses disposable sample holders with smart sensorchip (including all of the electrodes). The device requires only small(<100 μl) samples, typically sufficient to wet the sensors, or immersethem. The device determines fluid or solution identity and concentrationinstantaneously, and reports the results. The user is not required toinput any information about the fluid sample, however in some variationsthe user may indicate the expected identity and concentration of thesolution. In this case, the device may indicate that the sample matchesor does not match the expected mixture.

In some variations, the device or system may indicate if the solutiontested appears to have a component or a contaminant at dangerousconcentration, for example if the concentrations of certain componentsor contaminant are above those typically considered safe. Thus, thedevice (e.g., the processor) may include information about the safeconcentration ranges of known compounds, as well as information aboutcommon mixtures of compounds found in environmental samples. If thedevices or systems do not recognize the fingerprint of the testedsolution, then the device may also indicate this. This may occur if thefingerprint does not match the library of known fingerprints availableto the processor within a reasonable statistical range. In somevariations the system may provide the “closest match” and indicate aconfidence level (e.g., the statistical probability of the match, or itmay only indicate a match when the likelihood is above some thresholdlevel.

In-Line System or Device

FIG. 10 shows one embodiment of an in-line sensor configured to beattached in-line with a fluid source. In this example, the sensorsimultaneously (or essentially simultaneously) measures multipleparameters, including multiple complex admittances using multiplesensors. The sensor assembly is coupled directly in communication withthe solution being delivered to an industrial process of water supplysystem. For example, the sensor may be integrated or inserted in-linewith an tube, an pump, or the like. The sensor assembly is generallycoupled to a processor that can check the admittance spectroscopyfingerprint against a library of known admittance spectroscopy profiles.The system can then determine the identity or composition of the fluid,and report the substance identity, triggering an alert or an action(e.g., notification) if the solution exceeds a predetermined level of aparticular substance, or is missing a component (such as some addedagent: surfactant, chlorine, pH buffer, etc.). In some variations thesystem is programmed to have an expected solution composition for aarea. The system may also generally determine if one or more componentsdetected is outside of normal ranges, for say a geographical area.

For example, the system may be configured to monitor in particular thelevels of certain especially pernicious substances, and provide alertsif these substances are above a threshold (or are present in anyamount).

FIG. 11 shows another variation of an in-line sensor 1103 connected to asample line 1105. The sensor may be wirelessly or directly connected toa processor (not shown). FIG. 12 illustrates one variation of aprocessor and display 1203 for an in-line sensor such as the one shownin FIG. 11. The display may indicate the identity and the concentrationdetected (e.g., 2.4 mg/L) as well as the period of exposure or distance.The data may be displayed numerically, graphically, or both.

In any of the device variations described herein, when the device isassociated with a particular area or system, the device may beconfigured to customize the output based on area or system-specificparameters. For example, the system may be programmed with Gulf ofMexico data indicating what substances are normal and the associatedconcentrations. In some variations, the system may communicate with adatabase holding data unique to the area or the region. Access to knownbaselines for a geographical area can help scientists determine what achange, based on such things as time (or season), geographical area,currents etc is indicative of, and how the observed phenomenoninfluenced other systems. Even when system-specific parameters are notavailable to the device, the device may provide information (alerts,warning, etc.) indicating variance from typical values, for example,when a substance's concentration exceeds an expected value.

In any of these example, the system may include a log (which may be anon-volatile memory) storing the output of the system (e.g.,geographical location, temperature, turbidity, substance concentration,depth, etc.). The logged information may be connected to distributivelyaccessible database such as the Internet or an intranet.

Electrodes for Measuring Complex Admittance

The systems and devices for determining fluid components describedherein typically include a plurality of electrodes. Each electrodeincludes at least one fluid-contacting surface that is configured tocontact the fluid to be probed by the system or device, so that thefluid may interact with the surface of the electrode to form a dynamicequilibrium against the surface (e.g., the layered structure describedfrom FIG. 2). The surface interactions of a particular fluid arecharacteristic of both the composition of the fluid and the nature ofthe surface. As mentioned above, the systems described herein typicallycompare the complex admittance data from an unknown fluid against alibrary of known complex admittances. Thus, the electrode surfaces ofthe probe are controlled and maybe stereotyped, allowing comparison ofsampled complex admittance data against the known complex admittancedata without requiring substantial adjustments or normalizations of themeasured complex admittances.

In general, the devices and systems herein may include one or morearrays of electrodes for determining complex admittance. The electrodesare typically arranged so that pairs or combinations of electrodes maybe stimulated and measured in order to determine complex impedance oradmittance. Thus, a collection of electrodes may be arranged as a probe,a test cell, a conduit, a flow-though chamber, or the like. All of thesevariations are configured to bring the test solution (e.g., seawatersolution) into contact with the electrodes. A collection of two or moreelectrodes may also be referred to generically as a sensor. Thus, asensor may have multiple pairs of electrodes having fluid-contactingsurfaces that interact differently with the test fluid or solution.

The electrodes described herein may be referred to as admittanceelectrodes, and may be configured in any appropriate manner. The systemand devices described herein typically perform fluid admittancemeasurements in which at least 2 conductive or semi-conductiveelectrodes are used in contact with the fluid. In general, multipleelectrodes may be excited by a waveform signal having variable voltageand frequency.

Electrodes may be formed of any appropriate material, including metals,semiconductor materials, glassy carbon, carbon nanotubes, nanowires,porous materials, or the like. In some variations, the electrodes areformed from semi-conducting oxides (ITO), sulfates, phosphates, etc. atvarious degrees of doping or ceramics. In some variations, the materialsforming the electrodes are noble metals such as gold, platinum,palladium, rhodium, ruthenium, osmium, and iridium or their alloys. Theelectrodes may be formed of metals and alloys that generally areoxidation resistive such as niobium, tantalum or stainless steel, etc.or ones that form protective oxide layers such as titanium, aluminum,magnesium. The electrodes may be formed of metals with a thin protectivelayer such as SiO₂ that has been added over the electrode. Theelectrodes may be formed from combinations of any or all of the abovediscussed electrode materials.

For an electrical impedance sensor, multiple pairs of metal pads may beused. As discussed above, the electrodes used for admittancemeasurements may be polarizable (or fully polarized) electrodes. Theelectrodes may be formed of the same material, or of differentmaterials. Different metals and pairs of metal pads will provide uniqueresponses when exposed to compounds in solutions. For example if twoelectrodes each of gold, platinum and palladium may be used, and thefollowing combinations of metal pads can be used for sensing: Gold+Gold,Gold+Platinum. Gold+Palladium, Platinum+Platinum, Platinum+Palladium,and Palladium+Palladium.

The electrodes may be formed of the same material, but may havedifferent surface and bulk morphology, crystalline structure orgranularity, which may present a different surface interaction betweenthe fluid and the electrode. In some variations, the electrodes are ofthe same material, but the surfaces are chemically of physicallymodified and/or functionalized (chemically treated, coated,mono-layered, etched, plasma-etched, subjected to ion implantationprocess).

Pairs of electrodes may be formed of the same or different electrodes(e.g., electrodes having similar or different surface-fluidinteractions). For example, a sensor may include multiple pairs ofelectrodes in which each electrode in a given pair of electrodes areformed from the same materials or are formed from different materials.In some variations, the sensor includes electrodes having three or moreelectrodes of two or more compositions simultaneously.

In general, the electrodes may be formed from pads, traces, lamellae,interdigitated or other patterns of material deposited on an insulatingsubstrate.

The leads for connecting to electrodes may be formed from conductivematerial covered by a non-conductive layer to isolate them from theconductive fluid. In addition, part of the electrode surface may becovered with one or more insulating material, controlling the surface ofthe electrode exposed to the fluid. Thus, the electrode may includeopenings in a non-conductive layer that define the geometry of theworking surfaces exposed to the fluid.

In some variations the sensor includes electrodes for determining thecomplex admittance that are arranged as a probe. A probe may beconfigured for insertion into a solution or attachment to a vesselconfigured to contain the fluid.

In some variations of a sensor assembly, the sensor is a probe includingelectrodes having fluid-contacting surfaces arranged near each other. Insome variations the distance between electrodes forming pairs isapproximately the same. FIG. 13A illustrates one variation of a probeincluding six electrodes that each have a fluid-contacting surface 1301,1303, 1305, 1307, 1309. In this example, the electrodes are formed as alayer on top of a conductive element (shown in black) that is insulated.The insulation is open only over the fluid contacting surfaces of theelectrodes (shown as circles in this example).

In addition to the electrodes for determining admittance, a sensor mayalso include additional sensor elements, including sensors for measuringother characteristic fluid properties such as refractive index and/oroptical absorption (e.g., optical sensors, etc.). A sensor may alsoinclude additional sensor elements for determining bulk properties ofthe fluid, such as thermal conductivity or thermal diffusivity and/orwhether the fluid is steady or flowing. For example, FIG. 13B shows onevariations of a sensor including six admittance electrodes (arranged asshown in FIG. 13A) as well as a thermal anemometer flow sensor 1321 andan optical waveguide 1323 all incorporated into a single assembly. As inFIG. 13A, the traces shown in black are formed of thin films of a metalsuch as gold. The dots represent thin films of other metals deposited toform pads. The active areas of these sensors are the metal pads at theend of the traces. These pads are of different metals chosen to becompatible with immersion in typically encountered fluids. Theadmittance electrodes include an insulating coating except in the areaof the metal pads. This coating prevents contact of the sensor leadswith the conductive fluids but exposes a portion of the pads for directcontact with the fluid being tested. This sensor may be fabricated byknown semiconductor fabrication techniques, which may provide precisecontrol of the exposed surfaces of the admittance electrodes. Forexample, the probes may be produced by lithography on glass or othersubstrates. FIG. 13C shows a compact variation of the sensor array ofFIG. 13B. FIG. 13D is an alternative view of FIGS. 13B and 13C,indicated the leadframe region of the sensor array, which may be coupledor connected to the rest of the systems for determining fluidcomposition. The dimensions of the example shown in FIG. 13B are:10.5×8.5 mm, and it is integrated with lead frame as shown on the leftside of the figure. The compact embodiment shown in FIG. 13C isapproximately 2.5×3.875 mm. FIG. 13D shows the three resistortemperature detectors comprising a hot-wire flowmeter, a blow-up of thesensor region 1321.

The variations shown in FIGS. 13A-13D also illustrate the concept ofhighly reproducible disposable or single-use sensors. The sensor arraysmay be fabricated to a very high level of accuracy so that a new,previously unused sensor may be inserted in the system, used to test asolution, and removed. The used sensors may be recycled orreconditioned. For example, FIG. 14 shows a full panel of sensorssimilar to those shown in FIG. 13B that may be manufactured using metaldeposition and lithography. The overall dimensions of the panel ofsensor elements are 5×5 inches, and the individual sensors may be cutapart, or tested as part of a panel or strip (e.g., left connected, butused to test separate fluids).

The sensors described herein may also be configured as a measurementcell. A measurement cell may be configured so that the sensor forms thebottom of a chamber to contain the fluid, or the sensors may form a partof the wall of the chamber. In some variations, the measurement cell issealed until ready to use and is punctured by a needle to introduce thesample to be measured. The measurement cell may be sealed and evacuatedso that the sample will be drawn in by the differential air pressure. Ameasurement cell may be filled by capillary action of fluid through acapillary, micro-channel, wick or other sponge-like porous material. Insome variations, the cell is sealed and may contain a measured amount ofdry material or ionic fluid to introduce additional ions into thesolution to be measured. In this case, electrolyte may provide ions forimproved measurements of solutions that are in water or dextrosesolutions. The presence of the additional electrolytes may be includedin the analysis and recognition of the substance signature.

In some variations, the system includes a measurement cell in which asecond identical sensor or sensing site is exposed to a sample of astandard reference fluid such as normal seawater, in a sealed chamber,while the first sensor is exposed to sample of fluid under test. Theexcitation is applied to both sensors and the signals from both arecollected simultaneously and used for differential and/or ratiometricmeasurements.

The sensor or measurement cell may be compatible with automated use. Forexample, the measurement cell may be contained in a track or belt suchas that used to contain surface mount electronic components forautomated pick and place assembly. In the electronics industry, this isknown as “tape and reel”. In some variations, the measurement cell isconfigured to be part of a strip of measurement cells.

Signal Generator

In general, a measurement of the complex admittance is performed by theapplication of energy across a pair of electrodes, as illustrated above.Any appropriate signal generator (excitation source) may be used. Theapplied signal is typically less than 1 V (and typically less than0.5V).

The electrical impedance or admittance sensors are excited for detectionof admittance signals by applying energy across pairs of electrodes,wherein at least two of the electrodes are made of different metals.Admittance electrodes can be excited with a voltage waveform, voltage ata single fixed frequency, a set of two or more discrete frequencies,and/or a continuous sweep of frequency over a defined range. In somevariations, a DC bias current may also be applied on top of the ACexcitation to provide different measurement conditions. The data fromthese measurements provide signals related to both the surface propertyand bulk property and therefore the composition of the fluid contactingthe sensor. Thus, pairs of electrical impedance sensor pads, such asthose shown above in FIGS. 8 and 13A-13D, can be excited with ac currentat a single fixed frequency, a set of two or more discrete frequencies,and/or a continuous sweep of frequency over a defined range. For eachfrequency, one or more excitation amplitude levels may be applied to thesensor.

Thus, the signal generator may be configured to apply a singleexcitation frequency, or two or more different excitation frequencies.In some variations, the signal processor is configured to apply 10 ormore different excitation frequencies. As mentioned, the signalprocessor may be configured to continuously sweep the frequency from astarting frequency to an end frequency. The applied frequency may bevaried in defined steps from a starting frequency to an end frequency.In some variations, the swept frequency fluid admittance measurementsare taken in which the start frequency is lower than the end frequency,or the start frequency is higher than the end frequency.

In some variation, the excitation signal consist of a pure sine wave, anamplitude-modulated sine wave, a frequency modulated sine wave orphase-modulated sine wave. The applied time varying excitation signalwaveform may be a shaped waveform, such as a square waveform, atriangular waveform, a sawtooth waveform, an arbitrary function of timewaveform, or noise of various kinds such as white noise, pink noise offlicker noise.

The signal generator may apply energy to the admittance electrodes at asingle excitation voltage level, or at different excitation voltagelevels. For example, the signal generator may apply energy to theadmittance electrodes at 10 or more different excitation voltage levels.The ac excitation level may be at or below the thermal energy level inthe material to be tested. As mentioned, in some variations, a dc biasvoltage is applied in addition to the ac excitation.

In some variations, the system is configured and arranged, so that theexcitation signal and the measurement system are switched between pairsof electrodes. The switching may be controlled by a timer, a computer orother controller (e.g., microcontroller). The excitation signal level,as well as the excitation signal frequency, may be controlled(separately or jointly) by a timer, a computer or other controller(e.g., microcontroller).

In some variations, switching between excitation frequencies and/orpairs/sets of electrodes may be synchronized with the excitation voltageso that the switching takes place only at the predefined levels of theexcitation voltage, such as in case of the sine waveform whenexhilaration voltage is crossing zero level or when it reaches maximumor minimum or any other predefined level.

In some variations, the system may be configured so that a single signalgenerator is used. In some variations, the devices or systems mayinclude multiple signal generators. For example, the system may beconfigured to energize more than 2 electrodes or pairs of electrodes andmeasured simultaneously at the same frequency or at differentfrequencies.

In variations in which electrodes that are not used for admittancemeasurements are used (for example, where electric flow detectors suchas an anemometer), the same single generator may be used, or a separatesignal generator may be used.

In any of the variations described herein a controller may also be used.As mentioned, the controller may be a dedicated controller (such as amicrocontroller), or it may be a general-purpose computer adapted foruse. In some variations, the processor is integrated with thecontroller. The controller generally regulates the generation ofexcitation waveforms, as well as any additional sensors, and canregulate the switching between sensors. The controller may also collectdata from the sensors (including the admittance electrodes), storeand/or distribute data collected. Thus, a controller may be used forsensor and detector response conditioning and readout. The controllermay perform these functions itself, or it may coordinate performance ofthese functions by one or more sub-systems.

For example, the systems and devices described herein may include acontroller that controls digitization of sensor and detector responses.The controller may also filter and store digitized data. The controllermay also pre-condition the data (e.g., by amplifying it, smoothing orfiltering it, or subtracting it from a baseline, etc.).

In some variations, the system also includes a network interface forcommunication with one or more networks (which may be wired orwireless). The system or device may also include a user interface,including appropriate user inputs and outputs (displays/printers,keyboards, buttons, touchscreens, trackballs, etc.).

In addition, the system may also include one or more memory elements forstoring data, including storage of stimulation parameters and user-inputdata or observations. Stored information may also include a log of theperformed measurements. Any appropriate memory may be used, includingremovable media memory.

Processor

The systems and devices described herein also typically include aprocessor for analyzing the complex admittance (e.g., the admittancespectroscopy fingerprint) and comparing it to a library of known complexadmittances, and any additional characteristic parameter measured. Theprocessor may be electronic, and may include hardware, software,firmware, or the like. The processor may be a dedicated processor, or ageneral-purpose processor, and it may be local or remote. In somevariations, the processor is a distributed processor.

The processor may include a library of known parameter values. Theparameter values are coordinated to a solution having a known identityand/or concentration of components. The parameter values may include thecomplex admittance values measured from known fluids at definedcompositions and concentrations. The library may be stored in the memoryof the processor, or it may be accessible (remotely or locally) by theprocessor. For example, the library may be stored to a flash drive thatcan be updated periodically, or it may be located on a remote server andaccessed (or downloaded) by the system or device. In some variations thelibrary may be constructed or added to by the system or device,operating in a calibration mode.

In general, the library values are measured under similar conditions asthe test conditions. In particular, the complex admittance may bemeasured using a sensor that is configured similar or near-identicallyto the sensor used by the testing device or systems. Thus, the librarymay include complex admittance data that corresponds (or matches) themeasurement parameters of the admittance electrodes. For example, thelibrary admittance spectrographic fingerprint for a known composition offluid may be indexed by the same electrode pair (e.g., Au—Au, etc.) atthe same applied energy (frequency and energy level). The admittanceelectrodes making the measurement do not have to be the actualelectrodes used to determine the library reference admittance parameter,however, they should have approximately the same surface interaction,which may mean that the material forming the fluid-contacting surfacesand the geometry of the fluid-contacting surfaces may be approximatelyequivalent.

The fingerprint collected from the test device or system may includemore or a subset of the parameters in the fingerprints of the library.In general, the processor may use only a subset of the parameters (e.g.,the admittance spectroscopy and any other characteristic data) toidentify the composition of the test sample.

The processors described herein also typically include logic forrecognizing patterns between the test fingerprint and the library offingerprints. For example, the processor may include pattern recognitionalgorithms trained to recognize patterns corresponding to knownsolutions (e.g., solutions having a contaminants or mixtures ofcontaminants in a fluid). For example, the processor may include logicthat is configured to perform multi-dimensional data clustering, patternrecognition and/or neural network algorithms utilized for contaminantsrecognition from the training patterns. The processor logic is typicallyexecutable on any appropriate hardware, firmware or the like, asdiscussed above.

Algorithms for recognizing contaminants from multi-parametric sensordata may utilize sensor data from multiple channels to identifycompounds in a solution. The data set examined (e.g., the fingerprint)may include single data points, two dimensional curves, as well aspathways in multi-dimensional space to recognize specific compounds. Insome variations, software algorithms to detect contaminants from thedata input can be based: thresholds, peak fitting and analysis,clustering, and angles in 2D or multi-dimensional space. The processormay include neural networks that are trained on the library of knowncontaminant solutions, and interpolate between known data points todetermine the identity and concentration of contaminant or mixes ofcontaminants.

Any appropriate pattern-recognition or classification algorithm may beused by the processor to determine substance identity and/orconcentration. As described herein, in some variations the complexadmittance (and any other characteristic parameters measured) may berepresented as a vector, including multidimensional vectors of greaterthan 2^(nd) and 3^(rd) or der (n-dimensional). For example, thefingerprint taken from the sample may be curve fit to define theequation of the path taken by the curve through a multidimensional spacefor each compound versus concentration.

In some variations, the processor could include logic or algorithms forcomparing and/or recognizing fingerprints that has been hard coded intoa specialized chip (e.g., FPGA, etc) configured to run as hardwarerather than software. In this implementation, the specialized chip couldbe pre-programmed or trained with the compound patterns and could dohardware-level matching of sensor input patterns with thosepreprogrammed into the chip.

In some variations the pattern recognition logic may be referred to as“adaptive.” As used herein, the term adaptive generically refers to atrainable system or network (e.g., an adaptive neural network trained onthe library of fingerprints). In some variations, the patternrecognition logic may also be pre-trained, or fixed, and not “trainable”in a conventional sense. For example, a network may be constructed torecognize test fingerprints based on a library of fingerprint data.

A processor may generally receive the fingerprint “pattern” (e.g., thecomplex admittance data and any additional characteristic data), andcompare the pattern to the known library fingerprint patterns. Theprocessor may perform some or all of the following steps: patternacquisition, feature extraction, pre-processing, classification,regression description, pos-processing and communication of resultsand/or alerts. Pattern acquisition typically represents collection ofthe multi-dimensional sensor data. Feature extraction may involvedetermination of signal levels and extraction of primitives, such asvectors or curve descriptors. Pre-processing may be required for thefeature or descriptor values to be properly scaled and corrected for thedevice transfer function, including any nonlinearity of sensors andelectronics response. This may be an especially useful function ifneural network algorithms that require features to be scaled to unityare utilized. Post-processing typically interprets the output obtainedfrom the classification, regression and description steps. Based onidentification of the compound(s) in solution, this step may includeloading information on sensitivity of the environment or a technologicalprocess to the identified compound, and calculate the concentration andsends a message to either an other piece of industrial equipment, aserver interface or graphic user interface, which may generate an alert.

As mentioned, any appropriate pattern recognition algorithms may beused, including data clustering algorithms, statistical classificationalgorithms, neural network algorithms and structural analysisalgorithms.

A simplified example of the compound recognition process that aprocessor may perform is provided. In this example, a pair of metalelectrodes are exposed to a fluid, and the surface interaction betweenthe electrodes and the fluid can be investigated by energizing theelectrodes with an AC voltage or current and measuring the resultingcomplex current or voltage. As described above, when the stimulus signalis small enough for the system to respond linearly, the system can bedescribed in terms of complex AC impedance or admittance, e.g. real (x)and imaginary (y) response components can be measured.

The values of x and y as well as their relative magnitude changepredominantly with the electrical properties of the fluid flow andfluid-electrode interface, both of which are greatly affected by thecomposition of the flow. The change in these values is correlated to thenature of the fluid material and may be used to identify the particularmaterial.

In this example two circular coplanar gold electrodes of 0.32 mm indiameter are placed at 0.75 mm distance from each other on a wall of anon-conductive flow path. A 100 KHz AC voltage of 8 mV amplitude wasapplied across the electrodes in series with a 50 Ohm resistor and thevoltage drop across the resistor was measured using a Stanford ResearchModel SR830 lock-in amplifier. A PC was connected to the lock-inamplifier via RS232 interface with software recording the complexvoltage read by the lock-in approximately twice per second. The data wasplotted with the real part of the measured voltage value along theX-axis and the imaginary part along the Y-axis. In this experiment, dueto the naturally occurring noise, an average (x₀+iy₀) and standarddeviation (σ) were determined. A measured voltage value (x+iy) deviatingfrom the average value by |Δx+iΔy|>6σ in any direction on the XY chartis a statistically significant indication of a change in the fluid. Inthis case, arg(Δx+iΔy) defines the angular direction of the deviationvector. Two deviations Δx₁+iΔy₁ and Δx₂+iΔy₂ are statisticallydistinguishable if |Δx₁+iΔy₁|>6σ and |Δx₂+iΔy₂|>6σ and|Δx₁−Δx₂+i(Δy₁−Δy₂)|>6σ. The latter inequality defines the relationshipbetween the magnitude of the deviations and the angle between them forthe deviations to be distinguishable from each other.

Our experiments demonstrated (and can be explained theoretically) thatfor highly diluted additives to the standard fluid such as artificialseawater (ASW) flow the deviation distance from the pure ASW pointdepends on both concentration and molecular or ionic composition of theadditive, while the direction depends predominantly on the molecular orionic composition of the additive. For higher concentrations of theadditive both magnitude and direction of the deviation becomeconcentration-dependent in unique and distinguishable manner dependingon the nature of the additive.

In this example, for the demonstration of principle, pure 0.9% salinewas used as a proxy for ASW since it is a readily available standardsolution and solutions of other salts that are typical components of theASW were injected into a pure saline flow. The sensor is measuringflowing saline and a 1 ml of saline-diluted potassium chloride isinjected into the flow as a bolus dose. Once the “front” of the bolusreaches the vicinity of the electrodes, the complex current deviatesfrom its average value in pure saline and returns back when “trailingedge” of the bolus passes the vicinity of the electrodes, producing acharacteristic curve or signature. It can be seen that the “front” ofthe potassium chloride injection produces deviation from saline pointwhich is a nearly straight line at a distance far greater than the 6σthreshold of detection, which allows for accurate determination of thedirection of the deviation vector. For example, a linear regression ofthe measurement points from the 6σ threshold of detection to thedistance may be performed where residuals start exceeding 6σ. To makethe results more comprehensible, an angle between X-axis and thedirectional vector of the deviation based on the regression coefficientsmay be calculated, which was found in this example to be 74.4°.

When a 1 ml of saline-diluted magnesium sulfate bolus was injected intothe system, the measured complex voltage traced a curve very differentform the potassium chloride injection. As can be seen in FIG. 32, thedeviation from the saline point is more vertical, and of a smallermagnitude. The angle of the initial deviation calculated as explainedabove was found to be 85.6°.

Approximately 1 ml of plain deionized water was also injected into thesaline flow. The water generated a different curve, deviating in nearlyopposite direction from the previous injections. The angle of theinitial deviation for a water injection was found to be −118.2°.

The statistical uncertainty for these angle measurements was estimatedfrom the residuals of the linear regression used to calculatecoefficients determining the angles and for all three substances wasfound to be ±0.62°.

In some variations, the processor may be configured for recognition ofcompounds by continuously collecting data from the sensor(s) andchecking whether the value exceeds the 6σ threshold. Once the thresholdis exceeded, the software indicates that a different substance is likelypresent in the flow and starts linear regression on the consecutivelymeasured points, checking whether residuals exceed the 6σ threshold. Atthat point, the algorithm may conclude that the linear section of thedeviation curve is over and calculates a directional vector of the dataset being reduced. The directional vector can then be compared to valuespreviously determined for the vectors for specific compounds. In somevariations, the analysis can be done in terms of angles. For example, ifthe detected deviation falls within 74.4±0.62°—the injected bolus islikely potassium chloride, if it falls within 85.6±0.62° or −118.2±0.62°the injected substance is magnesium sulfate or water respectively. Ifthe angle is outside the known boundaries the algorithm reports theunknown substance in the flow. The same analysis may be performed usingmore than two dimensions, as mentioned above.

This simple algorithm can be adapted to recognize other substances thatproduce deviations in various directions by supplying the values for theexpected angles. Much more elaborate pattern recognition algorithms canbe applied to the differentiation and recognition of curves generated bythe sensing system in multi-dimensional space, as described, forexample, in Sing-Tze Bow, Pattern Recognition and Image Preprocessing,2002; M. S. Nixon, A. S. Aguado, Feature Extraction and ImageProcessing, 2002; and D. Maltoni, D. Maio, A. K. Jain, S. Prabhakar,Handbook of Fingerprint Recognition, 2002. For example, the recognitionsoftware can be based on artificial neural network and fuzzy logicalgorithms.

Although the majority of variations described above encompass systemsand devices in which the admittance spectroscopy is used to bothidentify the components of an unknown solution and to verify theconcentration of the components, in some variations, the system ordevice may be configured to determine just the identity of one or morecomponents of a solution.

One variation of the admittance spectroscopy methods described hereinprovides a special case for the determination the identity of one ormore components of a solution. At low concentration (e.g., under highlydilute conditions), the identity of one or a mixture of substances insolution may be readily determined, independently of the actualconcentration.

As mentioned above, the angular dependence of multi-dimensional signals,including electrical signals, may be determined for a particularelectrode pair based on the complex impedance. This may allow anapproximation of the identity of the compounds as the concentration ofthe compound(s) in solution increases from zero to a non-zero value.Expressed as a vector, the direction of the multi-dimensional signal'svector may reflect the identity of a compound (or identities in the caseof mixtures of compounds). We have found that for some compounds at lowconcentrations, the angles resulting from the in-phase and quadraturecomponents of the ac signal are independent of concentration. The angletherefore depends only on the nature of the compound, and not itsconcentration. Since the systems described herein are multi-parametric,and multiple signals are recorded for each substance or mixture ofsubstances in solution, the response may be represented by a vector insensor signal space.

Thus, in some variations, the measurements may be performed on thebackground of a known fluid. In this case, the identity may bedetermined as the concentration initially increases from zero in thecarrier, independent of the eventual final concentration. Thus thisvariation it may be convenient to place the origin for the frame ofreference at the end of signal vector generated for a known carrierfluid (e.g., saline, seawater, ASW) and operate with the signaldeviations from that point rather than with the full signal vectors andcall deviations from the know carrier fluid point “signals”. The sensorsignals may exhibit non-linear responses to substance concentration thatare different for components or compounds of different type andparameters. At very low component concentrations, the sensor signal willbe approximately proportional to the concentration (the non-linearresponse to concentration can be represented by a Taylor series in theneighborhood of a known carrier fluid point and only linear termretained). In this case the constant in the linear term can be called“sensitivity”, each coordinate of the response vector (r₁, r₂, . . .r_(n)), is proportional to concentration Δc and the vector coordinatesare s₁Δc, s₂Δc, . . . s_(n)Δc, or Δc*(s₁, s₂, . . . s_(n)), where s_(i)is sensitivity of the i-th sensor signal (or channel) and vector (s₁,s₂, . . . s_(n)) can be called “sensitivity vector” that will bedifferent for different types of substance. If in a substance #1 ofconcentration Δc the sensor produced response {right arrow over (r)} andin substance #2 at concentration ΔC response {right arrow over (R)} thecosine of angle between these two vectors can be calculated as:

$\frac{\overset{\rightarrow}{r} \cdot \overset{\rightarrow}{R}}{{\overset{\rightarrow}{r}}{\overset{\rightarrow}{R}}} = {\frac{\Delta \; c\; {\overset{\rightarrow}{s} \cdot \Delta}\; C\; \overset{\rightarrow}{S}}{\Delta \; c{\overset{\rightarrow}{s}}\Delta \; C\; {\overset{\rightarrow}{S}}} = \frac{\overset{\rightarrow}{s} \cdot \overset{\rightarrow}{S}}{{\overset{\rightarrow}{s}}{\overset{\rightarrow}{S}}}}$

where {right arrow over (s)} and {right arrow over (S)} are sensitivityvectors to substances #1 and #2 respectively. This considerationdemonstrates that for small concentrations of components the anglebetween the response vectors does not depend on concentrations anddepends only on sensor sensitivity to a particular substance, e.g.substance type. Therefore the angle between the response vectors can beused as a simple metric for distinguishing between the componentcompounds independently of their concentrations as long as theconcentrations are low. In the presence of naturally occurring noise,the angle between the vectors can only be calculated with finiteaccuracy determined by noise characteristics and sensitivity of thesensor response. For practical purposes, the angles can be calculatedbetween consecutively measured response vectors for a number ofmeasurements performed for a single substance and standard deviationcalculated for such dataset would define the smallest angle that can beresolved and thus the maximum achievable resolution. For higherconcentrations, the measured response of the sensors for a set ofconcentrations within range of interest for a given substance will bestored in memory in the form of a lookup table or polynomial fits, etc.This information will establish the calibration function:

{right arrow over (r)}={right arrow over (s)}(c)

for a particular substance, so that once the substance is identified theconcentration of it can be calculated from the sensor response:

c={right arrow over (s)} ⁻¹({right arrow over (r)})

This information is redundant for concentration calculations, so eitheronly one sensor channel can be used, several channels or absolute valueof the response vector, etc. depending on whether the noise isnon-correlated or partially correlated between the channels. Once thesubstance is identified at the time t, the sensor response can be pulledout of the database and instantaneous substance concentration can becalculated:

c(t)={right arrow over (s)} ⁻¹({right arrow over (r)}(t))

If the substance concentration exceeds predefined limits at any timeduring the sampling, the system can provide an alert. Once the newsubstance is identified, the response data can be traced back in time tothe point t₀ where the response first exceeded two standard deviationsfrom the baseline. The cumulative mass of the substance that has passedby the sensor (exposure) D(t) at a time t then can be estimated as:

D(t) = ∫_(t₀)^(t)q(t)c(t)t,

where q(t) is instantaneous volumetric flow measured by the flowmeter.

Data Communication Methods

In the various examples of systems and described herein, the componentparts of the system communicate with each other either by directlyconnecting to them (wiring) or wirelessly.

In some variations, the sensor communication channels (wires, opticalfibers, etc) may be incorporated into a sensor retention device, such asa cable. Communication pathways can be built into sample delivery tubingat the time of manufacture to provide a data pathway for transmittingsensor data. The incorporation of wires, conductive polymers and/oroptical fibers will provide a means for transmitting signals from asensor unit and/or processor unit to a receiver unit.

The systems and devices described herein may also communicate sensordata by an optical interface. Communication can be by either a fiberoptic link or free space optical signal link.

The systems and devices described herein may be integrated with one ormore other devices (or components of the system) through serial,Ethernet, wireless or optical communication means. For example, a deviceor system may be linked to another component through any common datacommunication interface including but not limited to the following:Ethernet, wireless, optical, and acoustic.

As mentioned above, communication of data from a sensor unit to a remoteprocessor may be performed by wire, wireless or optical means. In thiscase, the processor unit may be located physically at some distance fromthe sensor unit and the sensor signals communicated through acommunications link that includes but is not limited to the following:Ethernet, wireless, optical, acoustic, including ultrasound

In some variations the sensed fluid may be used by the device or systemas an RF antenna or conduit, taking care to not skew sensor results as aresult of signal transmission power. Thus, communication between theprocessor, data infrastructure and individual communication devices(PDAs, mobile phones, etc.) may be established wirelessly using.

Outputs

The systems and devices for determining the components of an unknownsolution described herein may include any appropriate output, includinginformation outputs (displays, printouts, alert lights, sounds, etc.),memory outputs (logs, digital records, etc.), control outputs (changingthe operation of a device based on the result), or any combinationthereof.

For example in some variations, the system or device includes a display.The display may be coupled to the device or located remotely to it. Thedisplay may indicate the results of the analysis, including indicatingthe identity and/or concentration of one or more components of thefluid. A display may also provide instructions, and system information(e.g., indicating how to operate the device), or error codes associatedwith operation.

Use of Admittance Spectroscopy with Other Sensor Modalities

The general concepts of multiparametric sensor measurements to determineidentity and concentration are herein developed in the particular caseof admittance spectroscopy. However, these same general concepts may beapplied using other modalities that detect properties reflectingcharacteristics of a particular solution composition. These additionalmodalities, examples of which are provided below, may be used incombination with the admittance spectroscopy devices and methodsdescribed herein.

The general principles of multiparametric analysis used to determineidentity and concentration applied herein may be expressed in a generalcase. For example, two different sensors respond to index of refractionand specific weight may provide multiparametric data that may be used todetermine identity and concentration. A sensor that responds to index ofrefraction or specific weight may have a measured response Δr thatdepends on both the nature of the introduced component (properties suchas MW, polarity, etc.), Δp, and its concentration, Δc. Thus: Δr=f(Δp,Δc). From a single measurement, concentration can be deduced if thenature of the component is known and vice versa. When multiple sensorsare used, the measured response is now a vector: Δr=(Δr1, Δr2), whichdepends on both nature the introduced component (Δp) and itsconcentration (Δc): Δr=f(Δp, Δc). For very low concentrationΔr≈(∂f(Δp,0)/∂c)*Δc. Value ∂f(Δp,0)/∂c does not depend on concentrationand can be called “sensitivity vector”. When the sensors are exposed totwo different substances, Δp1 and Δp2, at concentrations Δc1 and Δc2,respectively, the response vectors will be Δr1≈(∂f(Δp1,0)/∂c)*Δc1 andΔr2≈(∂f(Δp2,0)/∂c)*Δc2.

The cosine of angle between these two vectors is their scalar productdivided by their absolute values:

cos(φ)=(Δr1·Δr2)/|Δr1|/|Δr2|=[(∂f(Δp1,0)/∂c)*Δc1·(∂f(Δp2,0)/∂c)*Δc2]/(|(∂f(Δp1,0)/∂c)*Δc1|*|(∂f(Δp2,0)/∂c)*Δc2|)=(∂f(Δp1,0)/∂c)·(∂f(Δp2,0)/∂c)|/|∂f(Δp1,0)/ιc|/|∂f(Δp2,0)/∂c|.

Thus, in a generic sense, the angle between the sensitivity vectorsdepends only on the nature of substances Δp1 and Δp2 and is independentof concentration. The parameters informing the sensitivity andconcentration vectors may include the admittance spectroscopy data, butthey may also include additional sensor information, as mentioned above.Further, the dimensions of the system or method, e.g., the number ofparameters, may be as large as desired, while still keeping theprocessing necessary to a manageable (e.g., real-time) level.

Thus, a multiparametric system, including particularly the admittancespectroscopy systems described herein, may be used to determinehydrocarbon containing substances identity and concentration in, forinstance, seawater given an unknown solution including the hydrocarboncontaining substance (and other components). Although the complexadmittance and the use of admittance spectroscopy provide a rich sourceof data for the identification of unknown solutions, the use ofadmittance spectroscopy is also compatible with other sensor modalities.The use of additional sensor modalities may enhance the admittancespectroscopic methods, systems and devices described herein. Thesemethods may be particularly helpful in marine applications.

In addition to the admittance measurement techniques described above,the following sensor technology may also be used if needed for theparticular application: an electrochemical sensor (e.g., anelectrochemical potential sensor), a thermal sensor (e.g., a thermalanemometer sensor can be operated as fluid thermal diffusivity sensor),an optical sensor (e.g., a refractometry sensor, a transmission sensor,an absorbance sensor, a spectrometer (including a colorimeter), aturbidity sensor (nephelometer, a rheological sensor (e.g., aviscometer), an electrical property sensor (e.g., a capacitor sensor, apH sensor, a conductivity sensor, and an inductive sensor), and afluid-displacing or fluid-shearing (e.g., resonator) sensor. Fluidproperties and sensor technology to measure these properties are shownin the table below:

TABLE 1 Alternative sensor modalities Fluid Property Sensor ApproachComplex conductivity AC impedance spectroscopy or admittance Ionicproperties Electrochemical potential/spectrum Boiling point Pulsedthermal anemometry, Thermal diffusivity Pulsed thermal anemometry Indexof refraction Refractometry, fiber optic refractometer, optics IR, Vis.,UV absorption Transmission/Absorption Color Spectrometer, colorimeter,white light absorption spectra Viscosity Viscometer, resonator DensityViscometer, resonator Dielectric constant Capacitor, resonator Opacityor Clarity Optics, transmission, turbidity sensor Membrane permeabilitySelective sensors Ph Ph meter, MEMS ph sensor, chemical color changesensor, litmus paper Salinity Conductivity, density, refractive indexAir Optical, inductive, conductivity, thermal, Flow Flow meter, thermalanemometer

As an example of the application of different sensor modalities,consider a sensor that responds to the liquid's index of refraction andanother sensor that responds to liquid's conductivity. Assume that thereis a carrier fluid, such as saline (0.9% saline in water) solution, inwhich an additional component, such as contaminant, is dissolved.Further, assume that both sensors' responses reach values r¹ and r² whenan additional component is present in the liquid. Both the index ofrefraction and conductivity will depend on the added componentconcentration c and its “nature”: aggregate effect of parameters such asmolecular weight, polarity, ionic strength, etc.—p. The individualsensor's response is function of both concentration and nature of theadded component:

r=f(c,p)

therefore, the response of an individual sensor can only be calibratedto measure the concentration of a known component or determine what thecomponent is if the concentration is known. If the response from thesecond sensor is utilized, both the concentration and the nature of acomponent can now be measured:

r ₁ =f ₁(c,p); r ₂ =f ₂(c,p)

as this system of two equations with two variables can be solved in themajority of practical cases.

Two sensor responses can be treated as a 2D vector and the equations canbe written in vector form:

{right arrow over (r)}={right arrow over (f)}(c,p)

Notice that for components of a different nature p₁, p₂ . . . p_(n) endof this vector traces curves {right arrow over (r)}₁(c)={right arrowover (f)}(c, p₁), {right arrow over (r)}₂(c)={right arrow over (f)}(c,p₂) . . . {right arrow over (r_(n))}(c)={right arrow over (f)}(c, p_(n))as concentrations change and all curves at zero concentration start fromthe same point, which is the response in the carrier fluid. Thecomponents of interest these “concentration curves” or “signatures” canbe experimentally recorded and stored in a database. When an unknownsolution is measured—the response can be matched with the database ofsignatures.

This simple explanation can be expanded to more than two sensors withoutthe loss of generality. Additional sensors provide additional dimensionsto the vector and for the case of a single component this informationbecomes redundant. This redundancy is very useful in practice as theexperimental curves are always blurred by naturally occurring noise andany additional information improves overall resolution power of thetechnique.

One example of a combined electrical (admittance spectroscopy) andoptical system was illustrated above for the probe shown in FIGS.13B-13D. Another variation of an array of sensors (configured asmeasurement cell) is shown in FIGS. 15A and 15B, incorporating atransparent chamber through which fluid flows. In this example, a set ofoptical sources such as light emitting diodes (LEDs) that emit light atdiscrete wavelengths in the range of 250 to 1000 nm or more are embeddedacross from a set of matched detectors (matched to the emitting opticalsource), so that the light pathway spans the transparent fluid pathway.The optical detectors may be photo diodes or phototransistors withresponse matched to the optical sources (e.g., LEDs). An opaque holderfor the optical sources and detectors may be used to align them to eachother and limit the emitted/received light, and may include aperturesdetermining the viewing angle and aligning them with a fluid containeror (in this example) a flow pathway. A transparent chamber may beincluded with a cylindrical profile in which the fluid is placed orflows through, as illustrated in FIG. 15A and the end view shown in FIG.15B. The fluid chamber includes a fluid access point for an integratedelectrical sensor element such as that described in above (e.g., andshown in FIG. 13A).

The combination of the electrical sensors for determining the complexadmittance producing a total of 12 measurement channels (e.g., sixunique pairs of electrodes measuring both in-phase and quadraturecomponents) with the optical system producing up to 6 measurementchannels in this design produces a set of 18 independent measurementsthat are used to produce a unique pattern for each compound measured.The sensor system or array can be applied to the benchtop measurement ofcontaminants in an area in which they are being evaluated such as amarine laboratory or an aquarium.

Another mode of admittance sensor operation may include invocation ofthe electro-osmotic flow in the fluid under test. An electro osmoticflow creates motion in stagnant fluid or additional convective flow inthe flowing fluid that promotes fluid exchange and replacement in thevicinity of or at the sensor surface that eliminating or greatlyreducing any non-uniformity in the fluid or fluid flow under test. Thedetailed description of the phenomenon can be found in the followingpublications: Gonzalez, Ramos, Green, Castellanos, and Morgan, “Fluidflow induced by nonuniform ac electric fields in electrolytes onmicroelectrodes. ii. a linear double-layer analysis,” Phys Rev E StatPhys Plasmas Fluids Relat Interdiscip Topics, vol. 61, no. 4 Pt B, pp.4019-4028, April 2000; Green, Ramos, Gonzalez, Morgan, and Castellanos,“Fluid flow induced by nonuniform ac electric fields in electrolytes onmicroelectrodes. i. experimental measurements,” Phys Rev E Stat PhysPlasmas Fluids Relat Interdiscip Topics, vol. 61, no. 4 Pt B, pp.4011-4018, April 2000; and N. G. Green, A. Ramos, A. Gonzalez, H.Morgan, and A. Castellanos, “Fluid flow induced by nonuniform acelectric fields in electrolytes on microelectrodes. iii. observation ofstreamlines and numerical simulation.” Phys Rev E Stat Nonlin SoftMatter Phys, vol. 66, no. 2 Pt 2, p. 026305, August 2002.

In any of the variations described herein, the systems may include amixer or agitator before the sensor, in order to homogenize the fluidcomposition seen by the sensor(s). As mentioned above, mixing may beparticularly useful in the benchtop examples described herein, and mayalso be useful where the aqueous solutions include material suspended inthe solution.

Mixing of the test solution before it is probed by the sensor array mayimprove measurement accuracy. For example, the admittance sensorsinvoking elctro-osmotic flow described above may benefit from suchadditional mixing. Any appropriate mixer or method of mixing may beused. For example, a static fluid mixer such as that described in U.S.Pat. No. 3,286,992 may be used, for example, between an injection portand the sensor. In variations in which the sensor(s) are arrangeddownstream of an injection port, any non-uniform concentration profilesof the injected bolus in a carrier fluid in the vicinity of the sensormay be either taken into account via sensor calibration or physicallyeliminated at the point of measurement, including the use of a mixer. Inaddition, one or more filters (e.g., U.S. Pat. No. 4,601,820, and U.S.Pat. No. 5,992,643) may be used. Such filters may include woven wirefilter fabric with coarse mesh that brakes and randomizes flow path, andmay also be useful for mixing instead (or in addition to) a dedicatedstatic mixer. An active mixer may also be used. For example, the systemmay include a mixer that uses ultrasonic transducer such as apiezoelectric actuator that is located upstream from or near thesensor(s) or is integrated into the sensor assembly or substrate.

In one example of an admittance spectrographic system that includesanother sensing modality, a system using a disposable, multiparametricsensor element includes optical measurement channels and admittancesensors and a data acquisition and processing system. This systemmeasures a sample of a marine water or other compound, acquires a set ofmultiparametric sensor data and matches the patterns generated in thesensor data to previously obtained signatures of samples.

As mentioned, the optical data collected as part of the system mayinclude the refractive index and/or the absorption from at least one,but preferably 2 or more wavelengths. The sensor elements (which may beprobes, arrays, measurement cells, or the like), may include a housingthat places sensor elements in contact with the fluid to be tested. Insome variations, an optical pathway is included within the sensorelement for measurement of optical parameters such as refractive indexand absorption, as illustrated in FIGS. 15A and 15B. For example, apathway through the sensor housing may include an injection moldedoptical windows for optical access to the fluid. Examples of opticalsensors may include Light Emitting Diode (LED) sources and photodiodesand/or phototransistor detectors or any other applicable configurations.Optical sources consisting of solid state LED devices may have targetoptical wavelengths that can range from 250 nM to 1500 nM. For example,sources at 375 and 900 nM have used in a bench prototype. Othervariations may incorporate sources and detectors for additionalwavelengths in the range from 250 to 1500 nM or beyond to provideadditional data channels.

Systems including optical sensors may use broad band emission LEDsources, such as white LEDs may be used with a set of detectors eachincorporating a filter for a specific wavelength. For example, in somevariations, two or more optical sensor channels that measure thecompound's optical absorption at two or more different wavelengths. Insome variations, two or more optical sensor channels measure acompound's refractive index at two or more wavelengths. Opticaldetectors are typically matched to the LED sources for the specificwavelength. Optical filters that are external or internal to the sourceand/or detector may be used.

Electronics for signal conditioning may be used in any of theseexamples, including the combined electrical/optical systems, asmentioned above. For example, signals may be conditioned byamplification (e.g., operational amplifiers, lock in amplifiers),impedance analyzers, current to voltage converters, buffers, filters,and the like. The signal processing may occur before, as part of, and/orafter the data has been acquired. For example a data acquisition systemmay be used that includes: analog to digital converters, processors,specialized Application Specific Integrated Circuit (ASIC) circuits andField Programmable Gate Array (FPGA) devices for specialized functions.

The processor, including the recognition logic may be adapted tointerpret both the optical and the admittance data. Thus, both types ofdata may be use to compare obtained sensor patterns with known patternsto identify the compound and concentration.

Thus, additional modalities, such as optical measurements, may be usedto supplement the admittance spectroscopy measurements. During operationof the system described above, the LEDs may be switched on, one at atime while measurements are taken and then turned off. This avoidscrosstalk between the channels, reduces heating from the LEDs andincreases their lifetime.

The cylindrical nature of the flow path in the measurement cell maycreate a cylindrical lens with a fluid core and thus makes thetransmitted light sensitive to both the refractive index as well as theopacity of the fluid at a the given wavelength of the source anddetector. In this example, as well as the example shown in the sensorarray of FIG. 13B-13D, the optical system provides an additional 4 datachannels for sample identification by measuring at 4 differentwavelengths of light.

By applying a time varying excitation to an optical source such as anLED or laser, the resulting optical stimulus will have a time varyingcharacteristic. A frequency referenced detection system such as alock-in may be applied to the optical detector signals to improve thedetection by rejecting noise and spurious signals other than theexcitation frequency. If this frequency or frequencies are chosenproperly, interference from other systems may be minimized and thesensitivity of the technique improved over DC measurement techniques.

In some variations the sensor may be used as part of a cylindricaltransparent measurement cell that allows simultaneous measurement of thecombined effects of refractive index and absorption, as illustrated inFIG. 15A. Fluid samples may be measured in a cylindrical volume ormeasurement cell. Light emitting diode or other optical sources areconfigured to illuminate this cylindrical volume through a smallaperture and in a direction perpendicular to the cylindrical volume'saxis. A detector is located on the opposite side of the cylindricalfluid volume and aligned with the light source and the center of thefluid volume. The fluid properties of refractive index and absorption atthe specific wavelength of the source used will affect the intensity ofthe illumination at the detector and thus the measured signal. Changesin refractive index will affect the focusing or defocusing of the lightand impact the area of the detector illuminated and thus produce asignal proportional to the fluid refractive index. Any absorption willimpact the total intensity and thus also affect the measured signal. Bymeasuring with such sensors at 2 or more wavelengths, the absorption andrefractive index effects may be separated. However, for the purposes ofgenerating a set of unique sensor responses to produce a uniquesignature for a measured fluid, separation of these parameters may notbe necessary.

Optical absorption can be simultaneously measured at multiple opticalwavelengths spanning from infra-red to LW range. Absorption of specificwavelengths can be used to identify compounds in solution for compoundsthat have characteristic absorption bands. Supplying light thatcorresponds with an absorption region for a particular compound can beused to confirm the presence or absence of that material. The magnitudeof the absorption can also be used for concentration determination. Amulti-channel absorption system can have multiple different opticalsources such as LEDs each emitting a different wavelength and associatedwith a separate detector or a single detector and a switching system toturn on each LED in a sequence and measure the signal from the singledetector. Each different wavelength measured creates an additional datachannel that may be analyzed and used for compound detection andidentification.

Color detection may also be applied as a sensor modality. Many compoundsin solution will exhibit a particular color spectrum due to absorptionof some wavelengths of light. By applying light and detecting atmultiple wavelengths, the solution color can be determined. Thetechnique can be implemented using a 3 color led plus photodiode orphoto-transistor or by applying white light and detecting the resultingcolor spectra after the light has passed through the fluid. A colorsensitive detector chip such as the TAOS optical systems TS230D orsimilar may be employed. Alternatively, a set of red green and bluefilters may be placed between the light source and detectors and fromthe 3 values measured, the color coordinates of the fluid determined

Refractive index (RI) detection at multiple wavelengths may be used toseparate refractive index effects from evanescent wave effects. Bymeasuring the fluid refractive index at multiple wavelengths andcomparing the results, it is possible to separate the signal resultingfrom the fluid refractive index from evanescent wave effects that aremore sensitive to the fluid physical and chemical properties (evanescentwave sensors are described, for example, in P. Suresh Kumar et al., Afibre optic evanescent wave sensor used for the detection of tracenitrites in water; 2002 J. Opt. A: Pure Appl. Opt. 4 247-250, andPotyrailo, et al., Near-Ultraviolet Evanescent-Wave Absorption SensorBased on a Multimode Optical Fiber; Anal. Chem., 1998, 70 (8), pp1639-1645; DOI: 10.1021/ac970942v). As an example, the detector can usea color sensitive IC chip such as the TCS230 from TAOS Optics tosimultaneously measure the amplitude at multiple wavelengths anddetermine the absorption spectra or color of the solution.

Evanescent wave effects have been demonstrated to be sensitive tochanges in a fluid media. Using an uncoated fiber optic as a sensor willmeasure evanescent wave effects as there is no layer between thereflecting surface and the liquid interface. This can be applied tofiber optics, as well as any other refractive index method that involvesreflection changes from a media-fluid interface. The sensor can also beresponsive to evanescent wave fluorescence effects in the fluid.Selective coatings can be applied to the optical interface to provideselection of specific materials in the fluid. Measurements can be doneat a range of wavelengths from IR to UV and wavelengths can be chosenfor specific absorption or fluorescence regions to identify specificfluids. This can be applied to the measurement and identification ofcompounds in seawater.

Flow Sensors

Any of the systems and devices described herein may also include one ormore sensors for measuring flow. For example, a flow detector may beincorporated into a common sensor assembly as illustrated in FIGS.13B-13D. The sensor assembly in this example includes patternedelectrodes that form the electrical admittance sensors and the flowmeter. A transparent substrate can also be used as an optical pathand/or a transparent layer can be applied to the substrate to act as awaveguide for light. Alternatively, a fiber optic or other opticalwaveguide can be bonded to the substrate to provide a refractive indexsensor.

In some variations, the flow sensor is a hot wire anemometer flowdetector. A thin film, hot wire anemometer is shown in the FIG. 16 (avariation of which is incorporated into FIGS. 13B-13D). This sensormeasures flow by applying a very small amount of heat at one point in aflow stream, and from the change of temperature of a downstream sensor,the flow rate can be determined. In FIG. 16, thin film metal traces form3 resistors. With one upstream, and one downstream of the central heatedtrace, this sensor may be used in a differential configuration toimprove sensitivity and stability. It also has the capability ofmeasuring the direction of the flow.

The design in FIG. 16 includes a thin film anemometer produced by metaldeposition and lithography. It includes a set of 3 traces withdimensions of 1 mm long, 10 um trace width, 10 um trace-to-tracespacing.

In operation, the anemometer flow sensor electrodes may measure fluidthermal properties. For example, a hot wire anemometer such as thatshown above may be used to measure fluid flow (see, e.g., H. Bruun,Hot-wire anemometry: principles and signal analysis. Oxford UniversityPress, USA, 1995). In addition to or alternatively, if multiple wires ortraces are available, the flow rate is known, it may be used to measurechanges in the fluid thermal conductivity and/or heat capacity of thefluid. The basic idea of the hot-wire technique for the simultaneousmeasurement of the flow and the properties of fluid is that the usualcalibration based on King's law can be extended to a fluid property(such as compound concentration) so that the “calibration constants”become calibration functions of the fluid property. Accordingly, ifthere are two wires available for measurements, two calibrationfunctions, for which dependence of the fluid property is different, arepresent in King's law for each wire. The system of two King's equationsthen can be solved for two unknowns—the velocity and the fluid propertywith the accuracy determined by the wires implementation and signal tonoise ratio of the measurement system. The calibration coefficients inKing's law depend strongly on the thermal conductivity of the mixtureand thus are sensitive functions of compound's nature and concentration.A similar approach has been developed for the gas mixtures (e.g., P.Libby and J. Way, “Hot-wire probes for measuring velocity andconcentration in helium-air mixtures,” AIAA Journal, vol. 8, no. 5, pp.976-978, 1970.

Operation of an Admittance Spectrographic Device for Determining FluidComposition

In operation, any of the variations described herein may, generate afingerprint comprising the complex admittance data, as well as anyadditional data measured from the fluid. The fingerprint is typically adata structure that may be through of as an array, although it does nothave to be arranged as a matrix. Because the fingerprint will becompared to a library of known values (which may also be consideredknown fingerprints), the organization of the data within the fingerprintmay be stereotyped in format. For example, FIG. 17A conceptuallyillustrates one variation of an admittance spectroscopy fingerprinthaving 120 electrical channels, and thus at least 120 data points. Thisfingerprint is particularly useful for systems having, for example, sixunique pairs of electrodes. As described above, electrode pairs areunique when at least one of the electrodes in the pair presents adifferent fluid-contacting surface compared to fluid contacting surfaceson the other pairs (e.g., the composition or geometry of thefluid-contacting surface of the electrode is different). In FIG. 17A,the visual representation of the fingerprint data structure is indexedonline one side by the electrode pair, and six unique combinations ofelectrodes are used: Au—Au, Au—Pd, Au—Ti, Pd—Pd, Pd—Ti, and Ti—Ti. Tendifferent frequencies are examined using each electrode pair, as indexedhorizontally: 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 kHz. Asmentioned above, any appropriate frequency may be examined. In somevariations, additional parameters may also be varied (and could bevisualized as additional dimensions when represented as an array),including a DC offset, power applied, etc. For each electrode, and ateach frequency, both the in-phase 1703 and quadrature 1705 components ofthe complex admittance are determined. Thus, there are 120 differentparameters. Other variations of admittance spectroscopy fingerprints mayinclude more or fewer parameters, and may include additional parametersmeasured from other modalities, including any of those described above.For example, FIG. 17B illustrates a representation of one variation of afingerprint data structure that includes four optical channels (IR1,IR2, Vis, UV). The four optical channels may hold coupled absorption andrefractive index data.

Each of the parameters measured (or a subset of them) may be sampledmultiple times and the collection of values manipulated to provide thevalue entered in to the fingerprint (e.g., the mean, average, peak,minimum, median, etc. may be used).

An exemplary device such as the one shown in FIG. 9 was constructed as aprototype, and used to both generate known sample fingerprints, and toexamine unknown fluid samples to determine the identity andconcentrations of the samples.

In this exemplary device, a set of impedance sensor channels weresimilar to those shown in FIGS. 13B and 13D. With this set, thefollowing electrical (complex admittance) measurement channels areavailable: Au—Au, Au—Pd, Au—Ti, Pd—Pd, Pd—Ti, and Ti—Ti.

In the prototype, the complex ac response may be separated into real(in-phase) and imaginary (or quadrature) signals by a lock-in amplifierthus providing two data channels from each metal electrode pair andgiving a total of 12 impedance channels. The complex ac impedanceresponse of these electrode channels were measured using a lock inamplifier in current mode operating at a range of frequencies (10, 20,30, 40, 50, 60, 70, 80, 90 and 100 kHz).

In addition to the complex admittance measurements, in some testsoptical measurements were also made. For example, in some tests a fluidrefractive index sensor was used. In one variation, the RI sensoroperated at 910 nM and was constructed from an LED source and phototransistor detector coupled through a sharply bent section of opticalfiber that is immersed into a fluid. In addition, a fluid opticalabsorption sensor was used, operating at 375 nM consisting of a UV LEDsource coupled through the fluid flow, perpendicular to the flowdirection, to a photodiode detector. The optical source LEDS are drivenby adjustable current sources at levels of approximately 1-3 mA. Thisprovides low level light intensity to avoid detector saturation. At thisdrive level, the optical intensity applied to the fluid will be at most,a few microwatts per square cm.

In the exemplary device described above, the lock-in amplifier used hasX and Y output voltages that are measured by a National InstrumentssbRIO device and plotted in volts. The excitation voltage is set atV_(x)=21.21 mV RMS (30 mV-amplitude), and the complex admittance betweenthe sensor electrode in reciprocal Ohms is calculated as 6.09×10⁻⁴(X=iY), where X and Y are chart values. The complex current density isapproximately 1.83×10⁴ (X+jY) A/mm², where X and Y are chart values.

FIGS. 19A through 19L show the complex admittance plots of themeasurements over a set of various water samples from different sources.This set of samples is not exhaustive, but is merely intended toillustrate a subset of the relevant water samples initially tested. Thesensor was exposed to ware samples and the complex AC admittance wasmeasured between six different pairs of metal electrodes as shown in thelegend. The frequency steps for this particular set of measurementswere: 100, 200, 500, 1000, 2000, 5000, 10000, 20000, 50000, 100000 Hz,which appear as points on the plots. The plots for each sample producethe unique pattern depending of the sample nature and constituents ofthe sample, that can be matched with the database of standards orrepresentative samples measured earlier to classify the sample undertest.

The sensors used in this experiments is shown on FIG. 13B. Theconfiguration of this sensor is optimized for measurements in fluids ofmoderate ionic strengths or salinity. Measurements in de-ionized waterand in the injection grade sterile water for pharmaceutical applicationsare shown on FIG. 19A and FIG. 19B. Since both water samples haveextremely low admittance—the signal is predominantly pure noise, whichindicates very low ionic content in these water samples.

FIG. 19C and FIG. 19D show sensor response in two tap water samplescollected in two different California cities in San Francisco BayArea—Milpitas and Redwood City that are about 20 miles away from eachother. The patterns are still quite noisy, but considerably larger thenin de-ionized water and in the injection grade sterile water, whichindicates noticeably higher mineral content. The patterns however arevery similar. That indicates same water source, which turned out to bethe same Hetch-Hetchy reservoir. This also explains the low mineralcontent as primary source of water for Hetch-Hetchy reservoir is meltingsnow accumulated in winter time up in the Sierra.

FIG. 19E and FIG. 19F show sensor response in two tap water samplescollected at two different locations: zip codes 95129 and 95112 in thesame California city of San Jose about 8 miles away from each other.Considerably higher admittance indicates higher mineral content in bothsamples suggesting at least partial use of wells that tap theunderground aquifers. The response in the sample form zip code 95112 ishigher than from 95129 and has noticeably different pattern thatsuggests higher mineral content and different composition of minerals.

FIG. 19G shows sensor response in a de-gassed sample of a sparklingmineral water sample from Trader Joe's. In this sample the signal isconsiderably higher than in the most mineralized tap water samples. FIG.19H shows sensor response in marine water sample collected form SanFrancisco Bay. The response is two orders of magnitude higher than inthe most mineralized tap water samples, which is an expected result ofhigh salt content.

To demonstrate the ability of this technology to detect anddifferentiate various sources of marine water contamination for samplesof marine water contaminated by detergent and detergent-oil mixture attwo concentrations were prepared. The detergent used in theseexperiments was Simple Green™, which is a brand of cleaning productsproduced by Sunshine Makers, Inc., which is an approved Surface WashingAgent per the EPA's National Contingency Plan for oil spills since 1990.To emphasize the patterns produced by contamination the response inclean marine water sample from FIG. 19H is used as a baseline, which issubtracted from the admittance spectra collected from the contaminatedsamples. FIG. 19I and FIG. 19J show patterns resulted from detergentpresent in the marine water at concentrations of 0.0125% and 0.125%respectively on the same scale. Sensor response produces patterns thatdepend on detergent concentration and change not only in size, but alsoin general shape of the pattern.

FIG. 19K and FIG. 19L show patterns resulted from both the detergent andoil present in the marine water at concentrations of 0.0125% detergentand 0.0025% oil, and 0.125% and 0.025% oil respectively on the samescale. The pattern changes quite dramatically in presence of oil bothcompared to the sample where only detergent is present as well as afunction of oil concentration.

While the methods, devices and systems for determining composition of asolution using admittance spectroscopy have been described in somedetail here by way of illustration and example, such illustration andexample is for purposes of clarity of understanding only. It will bereadily apparent to those of ordinary skill in the art in light of theteachings herein that certain changes and modifications may be madethereto without departing from the spirit and scope of the invention.

1. A method of determining the identity and concentration of glycol ormixture of compounds containing glycol in non-polar fluids, the methodcomprising the steps of: contacting a first surface with the solution sothat a boundary layer of solution is formed on the first surface;polling the first surface to determine the surface interaction betweenthe first surface and the compound or mixture of compounds in thesolution at the boundary layer; and determining the identity andconcentration of the one or more compounds based on the surfaceinteraction.
 2. The method of claim 1, further comprising determiningthe identity and concentration of the one or more compounds based on thesurface interaction and the bulk properties of the solution.
 3. Themethod of claim 1, further comprising contacting a second surface withthe solution.
 4. The method of claim 1, wherein the step of contactingthe first surface with the solution comprises contacting the firstsurface in an aqueous solution.
 5. The method of claim 1, wherein thestep of contacting the first surface with the solution comprisescontacting the first surface with a solution.
 6. A method of determiningthe identity, concentration, or identity and concentration of one ormore compounds in a drinking water solution, the method comprising thesteps of: placing a pair of electrodes in contact with the aqueoussolution so that a boundary layer of aqueous solution is formed on afirst surface of one of the electrodes; applying electrical excitationbetween the pair of electrodes to determine a complex admittance at thefirst surface, wherein the applied electrical excitation results in avoltage that is below the threshold level for electrochemical reactionsat the first surface; and determining the identity, concentration, oridentity and concentration of one or more compounds in the aqueoussolution based on the complex admittance measured between theelectrodes.
 7. The method of claim 6, wherein the wherein the appliedelectrical excitation results in a voltage that is below 500 mV.
 8. Themethod of claim 6, wherein the step of determining the identity,concentration, or identity and concentration comprises simultaneouslydetermining the identity and concentration.
 9. The method of claim 6,further comprising recording the complex admittance at a plurality ofcurrent frequencies.
 10. The method of claim 6, wherein the pair ofelectrodes comprises conductive surfaces made of different materials.11. A system for making down hole oil well measurements and determiningthe identity of a components including at least one of water, saline,methane and oil content by admittance spectroscopy, the systemcomprising: a sensor comprising a plurality of electrodes havingfluid-contacting surfaces; a signal generator configured to provideelectrical stimulation at a plurality of frequencies for applicationfrom the fluid-contacting surfaces of the sensor; a processor configuredto receive complex admittance data from the sensor at the plurality offrequencies and to determine the identity, concentration, or theidentity and concentration of one or more compounds in the solution bycomparing the complex admittance data to a library of predeterminedcomplex admittance data.
 12. The system of claim 11, wherein thefluid-contacting surfaces of the electrodes of the sensor are formed ofa plurality of different materials.
 13. The system of claim 11, whereinthe fluid-contacting surfaces of the electrodes of the sensor are formedof a plurality of different geometries.
 14. The system of claim 11,wherein the sensor comprises at least three different fluid-contactingsurfaces formed of different materials, different size or differentmaterials and geometries.
 15. The systems of claim 11, wherein thesensor is configured to be single-use.
 16. The system of claim 11,wherein the processor comprises recognition logic configured todetermine the likeliest match between the complex admittance datareceived from the sensor and the library of predetermined complexadmittance data; wherein the recognition logic comprises an adaptiveneural network trained on the library of predetermined complexadmittance data.
 17. A system for monitoring an closed loop control offood and chemical manufacturing using admittance spectroscopy, thesystem comprising: a sensor comprising a plurality of electrodes havingfluid-contacting surfaces; a signal generator configured to providecurrent at a plurality of frequencies for application from one or morefluid-contacting surfaces of the sensor; a signal receiver configured toreceive complex admittance data from one or more fluid-contactingsurfaces of the sensor; a controller configured to coordinate theapplication of signals from the signal generator and the acquisition ofcomplex admittance data from the sensor to create an admittancespectrographic fingerprint of the solution; and a processor configuredto receive the admittance spectrographic fingerprint and to determinethe identity, concentration or identity and concentration of thesolution by comparing the admittance spectrographic fingerprint to alibrary of admittance spectrographic data comprising complex admittancedata measured from a plurality of known compounds and mixtures ofcompounds in a carrier solution at a plurality of frequencies and knownconcentrations.
 18. The system of claim 17, wherein the fluid-contactingsurfaces of the electrodes of the sensor are formed of a plurality ofdifferent materials.
 19. The system of claim 17, wherein thefluid-contacting surfaces of the electrodes of the sensor are formed ofa plurality of different geometries.
 20. The system of claim 27, whereinthe sensor comprises at least three different fluid-contacting surfacesformed of different materials, different geometries or differentmaterials and geometries.